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The Competitiveness of Nations in a Global Knowledge-Based Economy January 2003 Avrum Stroll A.P. Martinich
Epistemology Encyclopedia Britannica, Britannica 2003 Ultimate Reference Suite
Index
The phrase St. Anselm of
Index While a Platonic and Augustinian epistemology dominated the early Middle Ages, the translation of Aristotle’s On the Soul in the early 13th century had a dramatic effect. Following Aristotle, Thomas Aquinas (1225-74) recognized that there are different kinds of knowledge. Sense knowledge is what results from sensing individual things: thus, one sees a tree, hears the song of an oriole, and tastes or smells a peach. Thomas considered sense knowledge to be low-grade because it has individual things as its object and is also shared with brute animals. Sensation itself does not involve the intellect and is not properly speaking knowledge (scientia). It is characteristic of scientific knowledge to be universal; the more general in scope a piece of knowledge is, the better. This is not to diminish the importance of specificity. Scientific knowledge should also be rich in detail, and God’s knowledge is the most detailed. The detail, however, must be essential to the thing being studied and not peculiar to just some instances of that kind. Although Thomas thought that the highest knowledge humans can possess is knowledge of God, knowledge of physical objects is more attuned to human capabilities, and only that kind of knowledge will be discussed here. In his discussion of knowledge in Summa theologiae, Thomas Aquinas argues that human beings do not know material objects directly, nor are such things the principal object of knowledge. Knowledge aims at what is universal, while material things are individual and can be known only indirectly. Elaborating on the thought of Aristotle, Thomas claims that the process of thinking that accompanies knowledge consists of the active intellect (intellectus agens) abstracting (abstrahens) a concept from an image (phantasma) received from the senses. In one of Thomas’ accounts of the process, abstraction is the process of isolating the universal elements of an image of a particular object from those elements that are peculiar to the object. For example, from the image of a dog the intellect abstracts the ideas of being alive, being capable of reproduction, movement, and whatever else might be essential to being a dog. All these ideas are common to all dogs because they are essential to them. These ideas can be contrasted with the ideas of being owned by Dion and weighing five pounds, namely, with properties that vary from dog to dog. As stated earlier, Aristotle typically spoke of a form as being in the intellect of the knower, whereas the matter of an object is unintelligible and remains extramental. While it was necessary for Aristotle to say something like this in order to escape the absurdity of holding that a material object is in the mind in exactly the same way it is in the physical world, there is also something unsatisfying about it. Physical things contain matter as an essential element, and, if their matter is no part of what is known, then it seems that human knowledge is lacking. In order to counter this worry, Thomas revised Aristotle’s theory. He said that not the form alone but the species of an object is also in the intellect. A species is a combination of form and “common matter” (materia communis), where common matter is contrasted with individuated matter (materia signata vel individualis), which actually gives bulk to a material object. Common matter is something like a general idea of matter. Since every animal must have a body, it is not enough to conceive of an animal merely as something that is alive. Having flesh and bones, that is, being material, is part of the essence of being an animal. Of course this materiality, which is common to every animal, is not the same as the actual flesh and bone that constitute Fido - hence the distinction between common and individuated matter. This abstracted species resides in a part of the soul called “the passive intellect,” where it is described as being illumined by the active intellect. What this process amounts to is the isolation of those features of the intelligible species that are universal and necessary to it. Thus, to know what a human being is is to have abstracted the ideas of being rational and being capable of sensation, movement, reproduction, and nutrition and to have excluded the ideas of living in a particular place or having a certain appearance, all of which are not essential to being human. One objection that Thomas anticipated being raised against his theory is that it gives the impression that ideas, not things, are what are known. If knowledge is something that humans have and if what humans have in their intellect is a species of a thing, then it is the species that is known and not the thing. It might seem, then, that Thomas’ view is a type of idealism. Thomas had prepared for this kind of objection in several ways. His insistence that what the knower has in his intellect is a species, which includes matter, is supposed to make what is in the intellect seem more like the object of knowledge than an immaterial Aristotelian form. Also, scientific knowledge does not aim at knowing any individual object but at what is common to all things of a certain sort. In this, Thomas’ views are similar to those of 20th-century science. The billiard ball that John Jones drops from his porch is of no direct concern to physics. Even though its laws apply to John Jones’s ball, physics is interested in what happens to any object dropped from any height, just as what Thomas says about apples in general also applies to each individual apple. As assuaging as these considerations might be, they do not blunt the main force of the objection. For this purpose Thomas Aquinas introduced the distinction between what is known and that by which it is known. To specify what is known, say, an individual dog, is to specify the object of knowledge; to specify that by which it is known, say, the phantasm or the species of a dog, is to specify the apparatus of knowledge. The species of something is that by which the thing is known; but it is not itself the object of that knowledge, although it can become an object of knowledge by being reflected upon. The philosophical optimism of the 13th century dissolved as a consequence of the secular and ecclesiastical condemnations in 1270and 1277 of certain aspects of Aristotelian philosophy, and worries about Skeptical consequences began to emerge. While the philosophy of Thomas Aquinas was one of the targets of these condemnations, John Duns Scotus was also worried about the Skeptical consequences that could be elicited from the major competitor to Aristotelianism, the Augustinianism of Henry of Ghent (1217-93). According to Henry, God must “illumine” the human intellect on every occasion of its knowing. Not only could no good literal meaning be given to this sense of illumination, but the view also sounds as if all human knowledge were supernatural. Henry’s insistence that God’s illumination is a natural divine illumination did not persuade many people. While he accepted some aspects of Aristotelian abstractionism and also
held that there need to be some a priori principles of perception, principles
that he attributed to Augustine, John Duns Scotus (c. 1266-1308) did not rest
the certainty of human knowledge on either of them. He distinguished four different classes
of things that are certain: First, there are things that are knowable simply (simpliciter). These include both true identity
statements such as “ The second class of certainly known propositions consists of things knowable through experience, where “experience” has the Aristotelian sense of something that is encountered numerous times. The knowledge afforded by experience is grounded in the a priori epistemic principle that “whatever occurs in a great many instances by a cause that is not free is the natural effect of that cause.” It is important to note that Duns Scotus’ pre-Humean confidence in induction did not survive the Middle Ages. The 14th-century philosopher Nicholas of Autrecourt, who has been called “the medieval Hume,” argued at length that there is no necessary connection between any two events and that there is no rational justification for the belief in causal relations. The third class of certainly known propositions consists of things knowable that concern one’s own actions (de actibus nostris). Humans know when they are awake immediately and not through any inference; they know with certainty that they think (me intelligere)and that they hear and have other sense experiences. Even if a sense experience is caused by a defective sense organ, it remains true that one is aware of the sensuous content of the sensation: for example, one sees white even if one is mistaken in thinking that the seeing is caused by snow. The fourth class of certainly known objects consists of things knowable through human senses (per sensus). Duns Scotus said that humans learn about the heavens, the earth, the sea, and all that are in them. This last class of objects that are certainly known things seems to be posited without regard to the threat of Skepticism at all. Duns Scotus’ rendition of intuitive knowledge, however, has the purpose of forestalling the Skeptical move of interposing something between the knower and the thing known that might enable belief to deviate from its object. Intuitive knowledge is indubitable knowledge that something exists. It is knowledge “precisely of a present object [known] as being present and of an existent object [known] as being existent.” Further, the object of knowledge must be the cause of the knowledge. If a person sees Socrates before him, then, according to Duns Scotus, he has intuitive knowledge of the proposition that Socrates is white and that Socrates and his whiteness cause that knowledge. Intuitive knowledge contrasts with abstractive knowledge, such as knowledge of universals, for which the object need not be present or even existent. For example, for all one knows from contemplating the nature of dogs or unicorns, they are equally likely or unlikely to exist. It may appear that intuitive knowledge is absolute; either one has it or one does not. But that is not Duns Scotus’ doctrine. He held that there is imperfect intuitive knowledge of the past, which is more certain than abstractive knowledge but less certain than present intuitive knowledge. However plausible or implausible this may be, it is worth noting that Russell held the same view but expressed it by using the terms “knowledge by acquaintance” (intuitive cognition) and “knowledge by description” (abstractive cognition). There are several places in Duns Scotus’ account where Skeptical challenges can gain a foothold, for example, when he endorses the certainty of sense knowledge and when he holds that intuitive cognition must be of an existent object. William of Ockham (c. 1285-1349?) took his stand against the Skeptical challenge by radically revising Duns Scotus’ idea of intuitive cognition. Unlike Duns Scotus, Ockham does not require intuitive knowledge to have an existent object, and the object of intuitive knowledge need not be its cause. To the question “What is the basis for the distinction between intuitive and abstractive knowledge?” given that it is not the existence of the object and not a causal relation between an object and the knower, Ockham answered that they are simply different. His answer notwithstanding, it is characteristic of intuitive knowledge that it is unmediated. There is no gap between the knower and the known that might undermine certainty: “I say that the thing itself is known immediately without any medium between itself and the act by which it is seen or apprehended.” According to Ockham, there are two kinds of intuitive knowledge: natural and supernatural. In natural intuitive knowledge, the object exists, the knower judges that the object exists, and the object causes the knowledge. In supernatural intuitive knowledge, the object does not exist, the knower judges that the object does not exist, and God is the cause of the knowledge. In neither case is knowledge a relation; it is something a person has, a property of the person. Ockham recognized that God might cause a person to think that he has intuitive knowledge of an existent object when there in fact is no such object. But such a condition is not intuitive knowledge but a false belief. Unfortunately, in acknowledging that a person has no way to distinguish between genuine intuitive cognitions and divine counterfeits of them, Ockham has in effect lost the argument to the Skeptics. Later medieval philosophy followed a fairly straight path to Skepticism. John of Mirecourt was condemned in 1347 for holding among other things that there is no certainty of external reality because God could cause illusions to seem real. Nicholas of Autrecourt was also condemned in the same year for holding that only purely sensory reports of human experience are certain and that the only certain principle is that of contradiction, namely, that a thing cannot be and not be something at the same time. He denied that humans know that causal relations exist or that there are substances, two of many errors he credited to Aristotle, about whom he said, “In all his natural philosophy and metaphysics, Aristotle had hardly reached two evidently certain conclusions, perhaps not even a single one...” The link between Skepticism and criticism of Aristotle was fairly strong, and Petrarch, in On My Ignorance and That of Many Others (1367), cited Aristotle as “the most famous” of those who do not have knowledge.
From scientific theology to
secular science For most of the Middle Ages there was no split between theology and science (scientia). Science was knowledge that was deduced from self-evident principles, and theology received its principles from the source of all principles, God. In every way, theology was superior to the other sciences, according to Thomas Aquinas. By the 14th century the ideas of science and theology began to be separated. Roughly, theologians began to argue that human knowledge was much more narrowly circumscribed than earlier believed. They often exploited the omnipotence of God in order to undercut the arrogance and pretension of human reason. Their motive was to enhance the dignity of God at the expense of human reason, and in place of rationalism in theology, they promoted a kind of fideism. Gregory of Rimini (c. 1300-c. 1358) exemplified the growing split between natural reason and theology. According to Gregory, theology is not a science, and theological propositions are not scientific. In the new view of Gregory, who was inspired by Ockham, science deals only with what is accessible to humans through natural means, that is, through the ordinary operations of their senses and intelligence. Theology in contrast deals with what is accessible in some supernatural way. Thus, theology is not scientific. The role of theology is to explain the meaning of the Bible and the articles of faith and to deduce conclusions from them. Since the credibility of the Bible rests upon belief in divine revelation and revelation upon the authority of God, theology lacks a rational foundation. Further, since there is neither self-evident knowledge of God nor any natural experience of him, humans can have only an abstract understanding of what he is. Ockham and Gregory did not at all intend their views to undermine theology. For them, natural science is built on probabilities, not certainties. Since humans are fallible, their natural science is fallible, unlike theology, which is built upon propositions that have the authority of God. Unfortunately for theology, the prestige of natural science rose in the 16th century and skyrocketed in the 17th and 18th centuries; modern thinkers preferred coming to their own conclusions based upon experience and reason, even if these were only probable, to trusting the authority of anyone, even God. (This attitude has been called “the Faustian ethos,” after Goethe’s character Faust.) As the theologians tended to lose confidence in reason, other thinkers who had no or virtually no commitment to Aristotelian thought became the champions of reason and helped give birth to modern science. Modern philosophers as a group are usually thought to be purely secular thinkers. Nothing could be further from the truth. From the early 17th century until the middle of the 18th century, all of the great philosophers incorporated substantial religious elements into their work. Descartes, in his Meditations (1641), offered two different proofs for the existence of God, and he asserted that no one who does not believe in a cogent proof for the existence of God can have knowledge in the proper sense of the term. Benedict Spinoza began his Ethics (1677) with a proof for the existence of God, after which he expatiated on its implications for understanding all reality. And George Berkeley explained the stability of the sensible world by relying upon God’s constant thought of it. Among the reasons modern philosophers are mistakenly thought to be primarily secular thinkers is that many of their epistemological principles, including some that were intended to defend religion, were later interpreted as subverting the rationality of religious belief. The role of Thomas Hobbes (1588-1679) and John Locke might be briefly considered in this connection. In contrast with the standard view of the Middle Ages that propositions of faith are rational, Hobbes argued that propositions of faith belong not to the intellect but to the will. To profess religious propositions is a matter of obeying the commands of a lawful authority. One need not even understand the meanings of the words professed: an obedient mouthing of the appropriate confession of faith is sufficient. In any case, the linguistic function of virtually every religious proposition is not cognitive in the sense of expressing something that is intended to represent a fact about the world but rather to give praise and honour to God. Further, in contrast to the medieval view, according to which theology is the highest science, theology is not a science at all since its propositions are not susceptible to rational dispute. In An Essay Concerning Human
Understanding (1689), Locke further eroded the intellectual status of
religious propositions by making them subordinate to reason in several
dimensions. First, reason can
dictate what the possible content of a proposition allegedly revealed by God
might be; in particular, no proposition of faith can be a contradiction. Consequently, if the proposition that
Jesus is both fully God and fully man is contradictory, it cannot be revealed
and cannot be a matter of faith. Also, no revelation can be communicated
that contains an idea not based upon sense experience. Thus, What space, then, does faith occupy within the mansion of human beliefs? According to Locke, it shares a room with probable truths, those propositions of which reason cannot be certain. There are two types: claims about observable matters of fact and claims that go “beyond the discovery of our sense.” Religious propositions belong to each category, as do empirical or scientific ones. That Caesar crossed the Rubicon and that Jesus walked on water belong to the first type of probable proposition. That heat is caused by the friction of imperceptibly small bodies and that angels exist are propositions that belong to the second category. While mixing religious claims with scientific ones might seem to secure a place for the former, in fact it did not. For Locke also held that whether something is a revelation or not “reason must judge,” and more generally that “Reason must be our last judge and guide in everything.” Although this maxim was intended to reconcile reason and revelation - indeed, he calls reason “natural revelation” and revelation “natural reason enlarged by a new set of discoveries communicated by God” - over the course of 200 years reason repeatedly judged that alleged revelations had no scientific or intellectual standing. Although there is a strong religious element in modern thinkers, especially before the middle of the 18th century, the purely secular aspects of their thought predominate in the following discussion, because it is these that are of contemporary interest to epistemologists. Index
Impact of modern science on
epistemology Nicolaus Copernicus (1473-1543), a cleric, argued in On the Revolutions of the Celestial Spheres (1543) that the Earth revolves around the Sun. His theory was epistemologically shocking for at least two reasons. First, it goes directly counter to how humans experience their relation to the Sun; it is everyone’s prescientific view that the Sun revolves around the Earth. If science can overthrow such a belief, then scientific reasoning seems to lead to knowledge in a way that nonscientific reasoning cannot. Indeed, the nonscientific reasoning of everyday life may seem to be a kind of superstition. Second, his theory was shocking because it contradicts the view that is presented in several books of the Bible, most importantly the explicit account in Genesis of the structure of the cosmos, according to which Earth is at the centre of creation and the Sun hangs from a celestial ceiling that holds back the waters which once flooded the Earth. If Copernicus is right, then the Bible can no longer be taken as a reliable scientific treatise. Scientific beliefs about the world, then, must be gathered in a radically new way. Many of the discoveries of Galileo Galilei (1564-1642) had the same two shocking consequences. His telescope seemed to reveal that unaided human vision gives false or seriously incomplete information about the nature of celestial bodies. His mathematical formulations of physical phenomena seem to indicate that most sensory information may contribute nothing to knowledge. Like his contemporary, the astronomer Johannes Kepler, he distinguished between two kinds of properties. Primary qualities, such as shape, quantity, and motion, are genuine properties of things and are knowable by mathematics. Secondary qualities, namely, odour, taste, sound, colour, warmth, or coldness, exist only in human consciousness and are not part of the objects to which they are normally attributed. Both the rise of modern science and the rediscovery of Skepticism were important influences on René Descartes (1596-1650). While he believed that humans were capable of knowledge and certainty and that modern science was developing the superstructure of knowledge, he thought that Skepticism presented a legitimate challenge that needed an answer, one that only he could provide. The challenge of Skepticism, as Descartes saw it, is vividly portrayed in his Meditations. He considered the supposition that all of one’s beliefs are false, being the delusions of an evil genius who has the power to impose beliefs on people unbeknownst to them. But Descartes claimed that it is not possible for all of one’s beliefs to be false, for anyone who has false beliefs is thinking and knows that he is thinking, and if the person is thinking, then that person exists Nonexistent things cannot think. This line of argument is summarized in Descartes’s formula, “Cogito, ergo sum” (“I think; therefore, I am”). Descartes distinguished two sources of knowledge: intuition and deduction. Intuition is an unmediated mental seeing or direct apprehension of something experienced. The truth of the proposition “I think” is guaranteed by the intuition one has of one’s own experience of thinking. One might think that the proposition “I am” is guaranteed by deduction, as is suggested by the “ergo.” In Objections and Replies (1642), however, Descartes explicitly says that the certainty of “I am” is also based upon intuition. If one could know only that one thinks and exists, human knowledge would be depressingly narrow. So Descartes proceeded to broaden the limits of human knowledge. After showing that all human knowledge depended upon thought or reason, not sensation or imagination, he then proceeded to prove to his own satisfaction that God exists; that the criterion for knowledge is clearness and distinctness; that mind is more easily known than body; that the essence of matter is extension; and that most of his former beliefs are true. Few of these proofs convinced many people in the form in which Descartes presented them. One major problem is what has come to be known as the Cartesian circle. In order to escape from the possibility that an evil genius is deluding him about everything he believes, Descartes proves that God exists. He then argues that clearness and distinctness is the criterion for all knowledge because God does not deceive man. But, since this criterion is arrived at only after the existence of God has been proven, he cannot appeal to this criterion when he presents his proof for the existence of God; hence he cannot know that his proof is cogent. Index An Essay Concerning Human Understanding by John Locke (1632-1704) is often taken to be the first major empiricist work. Book I discusses innate ideas in order to deny that there are any; Book II discusses various genuine kinds of ideas; Book III discusses language with an emphasis on the meaning of words; and Book IV discusses knowledge and related cognitive states and processes. Innate ideas are ideas that humans are born with. Rationalist philosophers, like Descartes and Gottfried Wilhelm Leibniz (1646-1716), thought that there have to be such ideas in order to explain the existence of some of the ideas which humans have. One argument for innate ideas is that, while the ideas of blue, dog, and large, for example, can be explained as the result of certain sense impressions, other ideas seem unable to be attributed to sensation. Numbers, for example, seem to be outside the realm of sensation. Another argument is that some principles are accepted by all human beings, as, for example, the principle that out of nothing nothing comes. Locke did not think either of these arguments had any force. He held that all ideas can be explained in terms of sensation, and he set as one of his projects the task of providing such an explanation. Instead of directly attacking the hypothesis of innate ideas, Locke’s strategy was to refute it by showing that it is otiose and hence dispensable. In Book II of the Essay Locke supposes the mind to be like a blank sheet of paper that is to be filled with writing. How does the paper come to be filled? “To this I answer, in one word,” says Locke, “Experience.” He divides experience into two types: observation of external objects and observation of the internal operations of the mind. Observation of external objects is another description for sensation. Observation of the internal operations of the mind does not have its own word in ordinary language, and Locke stipulated “reflection” to designate it, because people arrive at ideas by reflecting on the operations of their own minds. Examples of reflection are perceiving, thinking, doubting, believing, reasoning, knowing, and willing. An idea is anything that the mind “perceives in itself, or is the immediate object of perception.” Qualities are the powers that objects have to cause ideas. Many words have dual senses. The word red, for example, might mean either the idea of red in the mind or the quality in a body that causes the idea of red in the mind. Some qualities are primary in the sense that all bodies have them. Solidity, extension, figure, and mobility are primary qualities. Secondary qualities are those powers that, in virtue of the primary qualities, cause the sensations of sound, colour, odour, and taste. Locke’s view is that the phenomenal redness of a fire engine is not in the fire engine itself, nor is the phenomenal sweet smell of a rose in the flower itself. Rather, certain configurations of the primary qualities cause phenomena such as the appearance of red or the taste of sweetness, and in virtue of these configurations the object itself is said to have the quality of redness or sweetness. But there is no resemblance between the idea in the mind (phenomenon) and the secondary quality that causes it. Locke claims, without justification, as George Berkeley was later to argue, that there is, however, a resemblance between primary qualities and the ideas of them. (Locke distinguishes a third sort of quality, e.g., the power of fire to produce a new colour or consistency in wax or clay, but he makes nothing of it.) Although Locke along with most distinguished modern philosophers repudiated Aristotelianism and the Scholasticism to which it gave rise, a doctrine of abstraction survives in his philosophy. Abstraction occurs when “ideas taken from particular beings become general representatives of all of the same kind.” That is, to abstract is to ignore the particular circumstances of time and place and to use an idea to represent all things of a certain kind. In Book IV Locke finally defines knowledge as “the perception of the connexion of and agreement, or disagreement and repugnancy of any of our ideas.” He also distinguishes several degrees of knowledge. The first is knowledge in which the mind “perceives the agreement or disagreement of two ideas immediately by themselves, without the intervention of any other,” which he calls “intuitive knowledge.” His first examples are such analytic propositions as “white is not black,” “a circle is not a triangle,” and “three are more than two.” But later he says, “The knowledge of our own being we have by intuition.” Relying on the metaphor of light as Augustine and others had, Locke says of this knowledge that “the mind is presently filled with the clear light of it. It is on this intuition that depends all the certainty and evidence of all our knowledge.” The second degree of knowledge occurs when “the mind perceives the agreement or disagreement of... ideas, but not immediately.” Some mediating idea makes it possible to see the connection between two other ideas. Proofs are things that show the mediating connections between ideas, and a clear and plain proof is a demonstration. Demonstrative knowledge is certain but not as evident as intuitive knowledge, says Locke, because it requires effort and attention to go through the steps needed to recognize the certainty of the conclusion. A third degree of knowledge, “sensitive knowledge,” approximates to what Duns Scotus and Ockham called “intuitive cognition,” namely, the perception of “the particular existence of finite beings without us.” Unlike medieval intuitive cognition, Locke’s sensitive knowledge is less certain than his intuitive or demonstrative knowledge. Beneath knowledge is probability, which is the appearance of agreement or disagreement of ideas with each other. Etymologically, probability is a likeliness to be true, and it guides in matters “whereof we have no certainty.” Locke suggests that probability rests upon the testimony of others and, like knowledge, comes in degrees, which depend upon the likely veracity of the sources of the proposition. The highest degree of probability attaches to propositions endorsed by the general consent of all people in all ages. Locke may have in mind the virtually general consent of his contemporaries in the proposition that God exists. But he explicitly mentioned beliefs about causal relations, which are not perceived but inferred. To argue from such beliefs is called “an argument from the nature of things.” The next degree of probability or assurance in probable propositions attaches to matters that hold not universally but for the most part, such as that persons prefer their own private advantage to the public good. This sort of proposition is typically derived from history. The next degree of probability or assurance attaches to claims about specific facts, for example, that a man named Julius Caesar lived a long time ago. Problems arise when testimonies conflict, as they often do, but there is no simple rule or set of rules that instructs one how to resolve such controversies. In addition to these probabilities, all of which concern particular matters of fact, there are also probabilities about things that are not within the power of the senses. The existence, nature, and operation of angels, devils, microbes, magnets, and molecules all fall into this class. It is important to recognize that for people as scientific as Locke, who was a member of the Royal Society, all of these were part of the same class. It took many centuries to separate science from religion and superstition. Index Locke is part of a philosophical tradition called empiricism, that is, the view that the sole or at least the major source of human knowledge is sensory experience. George Berkeley (1685-1753) was the next great adherent of empiricism. In his major work, Treatise Concerning the Principles of Human Knowledge (1710), he divides ideas into three types: Ideas that come from sense correspond to Locke’s simple ideas of sensation. Ideas that come from “attending to the passions and operations of the mind” correspond to Locke’s ideas of reflection. Ideas that come from compounding, dividing, or otherwise representing ideas, correspond to Locke’s compound ideas. An apple, for example, is a compound of the simple ideas of colour, taste, smell, and figure associated with it. In addition to ideas, what exists are spirits or souls or minds. By “spirit,”
The question whether a tree falling in a virgin forest makes a sound is
inspired by However strange his doctrine may initially sound,
If one objects that the second premise of the syllogism is false on the
grounds that people sense things, not ideas,
A consequence of this argument is that Locke’s distinction between primary and secondary qualities is spurious. Extension, figure, motion, rest, and solidity are as much ideas as green, loud, and bitter are; there is nothing special about the former kinds of ideas. Furthermore, matter, as philosophers conceive it, does not exist and indeed is contradictory. For matter is supposedly unsensed extension, figure, and motion, but since extension, figure, and motion are ideas, they must be sensed. On another matter, the doctrine of abstraction,
Although Hume aspired to be the Index Hume has a twofold division of perceptions: impressions and ideas. Impressions are perceptions that enter with “most force and violence.” Ideas are “faint images” of impressions. Hume thinks the distinction so obvious that he demurs from explaining it at any length. Impressions are felt; ideas are thought, he indicates in his summary explication. He also concedes that, although one can always discern the difference between an impression and an idea by its force, sleep, fever, and madness sometimes produce ideas that approximate to the force of impressions, and certain impressions approach the weakness of ideas. But such occasions are rare. The distinction has a problem that Hume did not notice. The impression (experience) of anger has an unmistakable quality and intensity, but it is not the case that the idea of anger always makes a person feel angry. Thinking of anger no more guarantees being angry than thinking of the idea of happiness guarantees being happy, even if thinking happy thoughts tends to make people happy. So there is a difference between the experience of anger and the idea of anger that Hume’s philosophy does not capture. In addition to impressions and ideas, perceptions can be divided into the
categories of simple and complex. Whereas simple perceptions are not
subject to further separation or distinction, complex perceptions are. For example, apples, although unitary
objects in one view, are in fact complex perceptions; they are divisible into a
certain shape, colour, texture, and aroma. It is noteworthy that for every simple
impression there is a simple idea that corresponds to it and differs from it
only in force and vivacity, and vice versa. So, corresponding to the impression of
red is the idea of red. This does
not hold true in general for complex perceptions. Although there is a correspondence
between the impression of an apple and the idea of an apple, there is not always
a correspondence between impressions and ideas. There is no impression that corresponds
to the idea of Pegasus or a unicorn; these complex ideas do not have a correlate
in reality. There are also complex
impressions that do not have a corresponding idea. A traveler who has seen an extensive part
of Because of their correspondence, there seems to be a special connection between simple impressions and simple ideas: the former cause the latter. Hume deduces this on the following grounds. A simple impression always precedes the corresponding idea, and the idea invariably follows the conjoined impression. Thus, because of the temporal priority of impressions and the constant conjunction of impressions and ideas, Hume concludes that impressions cause ideas. There are two kinds of impressions: sensation and reflection. Sensation “arises in the soul originally from unknown causes.” Hume says little more about sensation because discussion of it belongs to anatomists and scientists. (Many late 20th-century philosophers do not accept this division between philosophy and anatomy.) To explain reflection is rather complicated because it derives from a complex mental operation. After people feel heat or cold, thirst or hunger, pleasure or pain, they form ideas of heat or cold, thirst or hunger, pleasure or pain. And, following the formation of these ideas - at a third stage of cogitation - they form from the ideas the second kind of impressions: impressions of “desire and aversion, hope and fear.” These impressions are the result of reflecting on ideas caused by sensation. Since imagination can divide and assemble disparate ideas as it will,
some explanation is needed for why the mind seems to run in predictable
channels. Hume says that the mind
is guided by three principles: resemblance, contiguity, and cause and effect.
Thus a person who thinks of one
idea is likely to think of another idea that resembles it. For example, a person’s thought, if one
accepts Hume’s account, will run from red to pink to white, or from dog to wolf
to coyote. Hume also uses the
principle of resemblance to explain how general ideas function. Hume agrees with
Although people gain much information from their impressions, most matters of fact depend upon reasoning about causes and effects, even though people do not directly experience causal relations. What, then, are causal relations? According to Hume they have three components: contiguity of time and place, temporal priority of the cause, and constant conjunction. In order for x to be the cause of y, x and y must exist adjacent to each other in space and time, x must precede y, and x and y must invariably exist together. There is nothing more to the idea of causality than this; in particular, people do not experience and do not know of any power, energy, or secret force that causes possess and that they transfer to the effect. Still, all judgments about causes and their effects are based upon experience. To cite examples from An Enquiry Concerning Human Understanding (1748), since there is nothing in the experience of seeing a fire close by which logically requires that one will feel heat, and since there is nothing in the experience of seeing one rolling billiard ball contact another that logically requires the second one to begin moving, why does one expect heat to be felt and the second ball to roll? The explanation is custom. In previous experiences, the feeling of heat has regularly accompanied the sight of fire, and the motion of one billiard ball has accompanied the motion of another. Thus the mind becomes accustomed to certain expectations. “All inferences from experience, therefore, are effects of custom, not of reasoning.” Thus it is that custom, not reason, is the great guide of life. In short, the idea of cause and effect is neither a relation of ideas nor a matter of fact. Although it is not a perception and not rationally justified, it is crucial to human survival and a central aspect of human cognition. Index One of the cornerstones of philosophy from Plato to
Index
Relations of ideas and matters
of fact Human thought concerns two kinds of things: relations of ideas and matters of fact. Relations of ideas can either be intuited, that is, seen directly, or deduced from other propositions. That a is identical with a, that b resembles c, and that d is larger than e are examples of propositions that are intuited. The opposites of true propositions expressing relations of ideas are contradictory. Arithmetic and algebra are the subjects about which there can be the most certainty. In his Treatise Hume says that geometry is almost as certain as these, but not quite, because its original principles derive from sensation, and about sensation there can never be absolute certainty. He revised his views about geometry later, and in the Enquiry he puts geometry on an equal footing with the other mathematical sciences. In contrast with relations of ideas, matters of fact are derived from experience. Experience, however, would be quite limited if it did not include causal relations, which go beyond what is experienced. Index Hume’s discussion about relations of ideas and matters of fact gives the impression that he thought that human knowledge is possible. Relations of ideas seem to be the object of knowledge, while matters of fact seem to be the object of probability. In Part II of the Treatise he denies this and argues forcefully for Skepticism. Until the beginning of Part IV of Book I of the Treatise, there is little or no hint of Skepticism. The distinction between knowledge (of the mathematical sciences) and probability (of matters of fact) seems to presuppose that there is knowledge. But one then discovers that Skepticism undermines it all. Although the rules of science are certain and infallible, the application of those rules by humans is uncertain and fallible because humans are prone to error. It does no good for a person to try to check his chain of reasonings because the process of checking is no more immune to error than the original calculation. How can one know that the checking process was performed correctly? And, if the checking procedure seems to identify a mistake in the original calculation, how can one determine whether the error is in the original or in the seeming identification of an error? Adding a checking procedure is in one respect worse than leaving the original calculation alone. It introduces a second event, which, like the original calculation, is possibly flawed. And it is more probable that one of two possibly flawed events is flawed than either one of the two alone. “By this means,” Hume says, “all knowledge degenerates into probability.” Another way to see this consequence is to consider that reason is a cause of truth. But, since all causal relations are probable, not certain, all human reasoning is at best probable. If one thinks further about the matter, the probability of knowledge
diminishes and doubt increases. Each judgment of the probability of some
judgment introduces further reasons for doubt and thus lowers the overall
probability. The joint probability
of p and q is lower than the probability of p; and the joint probability of p,
q, and r is lower than the probability of p and q. Ultimately, “when I proceed still
farther, to turn the scrutiny against every successive estimation I make of my
faculties all the rules of logic require a diminution, and at last a total
extinction of belief and evidence.” If one should say, “Surely, you are
kidding,” Hume’s answer would be a
beguiling one: In a sense, “yes,” for nature has so made human beings that they
cannot in fact be skeptical even though the argument for Skepticism is cogent.
As Hume says in his Enquiry, people conduct their lives for
the most part governed by custom and nature, not reason. Skepticism is true even though there are
no Skeptics, because, as in
There is another way of expressing Hume’s position. If one examines the grounds that human beings have for trusting their reasoning, one will not be able to find rational grounds. Reason cannot be rationally grounded, and the ground of rationality is wholly nonrational: “belief is more properly an act of the sensitive, than of the cogitative part of our natures.” Some people have tried to make short shrift of Skepticism by pointing out that if the Skeptic recognizes his arguments to be rationally compelling, then he must recognize the sovereignty of reason and hence the falsity of Skepticism. Hume points out that the battle against Skepticism cannot be won in this way. Skepticism is a refutation of the claims of reason. As such, one assumes the truth of rationalism in order to show that it is contradictory and hence false. In other words, Hume’s proof is a reductio ad absurdum argument against belief in rationality. The Skeptical argument proceeds by arguing that, if rationalism is true, then it is not rational to be rational. Since the consequent is contradictory, the assumption that rationalism is true must be false. Thus, rationalism is false. Hume has been called “the complete Pyrrhonist,” but Hume himself denied that he was one, in large part because he did not distinguish between Pyrrhonism and Academic Skepticism, both of which, according to him, advocate the suspension of belief even as one conducts one’s ordinary affairs. Hume thought such a program impossible for human beings: humans are condemned to believe. Unlike the Pyrrhonist, Hume does not suspend judgment or abandon reason. He judges according to reason because it is his nature to do so even though Skeptical arguments against reason are cogent. This philosophical schizophrenia - the use and trust in reason coupled with the recognition that rationality has no rational justification - is part of what Hume calls “mitigated Skepticism.” Another part of it is restricting one’s investigations to topics that are within the “narrow capacity of human understanding,” namely to experience and the mathematical sciences. Given his Skepticism, one might wonder whether it could be directed against Hume’s own positive doctrine. It can. At the end of Part I of his Treatise Hume says, “Can I be sure, that in leaving all establish’d opinions I am following truth; and by what criterion shall I distinguish her, even if fortune shou’d at last guide me on her foot-steps? After the most accurate and exact of my reasonings, I can give no reason why I shou’d assent to it; and feel nothing but a strong propensity to consider objects strongly in that view, under which they appear to me.” Ultimately one judges according to custom and the way nature dictates one must judge. The Enquiry Concerning Human Understanding is intended to be an accurate description of how people judge, not a justification of it. Idealism is often defined as the view that everything which exists is mental; that is, everything is either a mind or depends for its existence upon a mind, as do ideas and thinking. Immanuel Kant (1724-1804) was not strictly an idealist according to this definition, although he called himself a “transcendental idealist.” On his view, humans can know only what is presented to their senses or what is contributed by their own mind. Every sensory experience is a mixture of a sensory content, which is simply given to a person, and a spatial and temporal form, which is contributed by the mind itself. Further, if one formulates a sensory experience into a judgment, then the mind also contributes certain additional objective features: the judgment incorporates ideas of something being a substance or quality of that substance, ideas of one thing causing another, or one thing being related by necessity or by accident to another. In short, the raw data of sensory input is only a small part of what constitutes human knowledge. Most of it is contributed by the human mind itself; and, so far as human knowledge is concerned, rather than the mind trying to accommodate itself to the external world, the world conforms to the requirements of human sensibility and rationality. Kant compared his radical reorientation of the way philosophers ought to study human knowledge to the Copernican revolution in astronomy. Just as the Earth revolves around the Sun, contrary to common sense, objects conform themselves to the human mind, contrary to common sense. Kant’s idealism notwithstanding, he also believed that a world existed
independent of the human mind and completely unknowable by it. This world consists of
things-in-themselves, which do not exist in space and time, are not organized in
causal relations, and so on, because these are elements contributed by the human
mind as conditions for knowing. Because of his commitment to realism
(minimal though it may be) Kant was disturbed by
Kant’s goal, as developed in Critique of Pure Reason (1781), was to
supplant Kant believed that all objects of sensation must be experienced within the limits of space or time. Thus, all physical objects have a spatiotemporal location. Because space and time are the backdrop for all sensations, he called them pure forms of sensibility. In addition to these forms, there are also pure forms of understanding, that is, categories or general structures of thought that the human mind contributes in order to understand physical phenomena. Thus, every empirical object is thought to have some cause, to be either a substance or part of some substance, and so on. The structure of judgments finally leads to the question of what properties the propositions that express judgments (or knowledge) have. From a logical point of view, the propositions that express human knowledge can be divided according to two distinctions. First is the distinction between propositions that are a priori, in the sense that they are knowable prior to experience, and those that are a posteriori, in the sense that they are knowable only after experience. Second is the distinction between propositions that are analytic, that is, those in which the predicate is included in the subject, and those that are synthetic, that is, those in which the predicate is not included in the subject. Putting the terms of these two distinctions together yields a fourfold classification of propositions. (1) Analytic a priori propositions include “All bachelors are unmarried” and “All squares have four sides.” (2) Analytic a posteriori propositions do not exist, according to Kant, because, if the predicate is conceptually included in the subject, the appeal to experience is irrelevant and unnecessary. Also, the negation of an analytic proposition is a contradiction; but, because any experience is contingent, its opposite is logically possible and hence not contradictory. (3) Synthetic a priori propositions include “Every event has a cause” and “7 + 5 = 12.” Although it is not part of the concept of an event that it be a cause, it is universally true and necessary that every event has a cause. And, because 12 is a different concept from seven, five, and plus, it does not include any of them singly or jointly as a part of it. (4) Finally, synthetic a posteriori propositions include, “The cat is on the mat” and “It is raining.” They are straightforwardly and uncontroversially empirical propositions that are not necessary and are discoverable through observation. Kant’s view that human experience is bounded by space and time and that it is intelligible only as a system of completely determined causal relations existing between events in the world and not between the world and anything outside of it has the consequence that there can be no knowledge of God, freedom, or human immortality. Each of these ideas exceeds the bounds of empirical experience and hence is banished from the realm of reason. As he said, he “found it necessary to deny knowledge, in order to make room for faith.” G.F.W. Hegel (1770-1831) developed his epistemology pari passu with ontology. Since his positive views are difficult and replete with technical terms, his epistemology is not susceptible of summary here. Some of his criticisms of earlier epistemological views, however, should be mentioned since they helped to bring modern philosophy to a close. Empiricism takes cognition of particular sensed objects as the foundation for knowledge. But, Hegel argues, no sensation is purely particular. For every sensation consists of something that has a certain feature, quality, or feel, and this feature, quality, or feel is something common to other sensations and hence not particular. Also, all knowledge must be expressible in language, and all fully articulated language uses predicates, which express concepts. Even if the empiricist attempts to represent his knowledge with a single, purely demonstrative word, say, “this” or “now,” his view is contradictory. For “this” is common to any indicated object, and “now” can be used to refer to any time. An analogous argument holds against anyone who, like Descartes or Kant, wants to begin with the referent of “I.” Another mistake common to empiricism and rationalism is to think that knowledge requires a correspondence between a person’s beliefs and reality. The search for such correspondence is logically absurd since every such search ends with some belief about whether the correspondence holds or not, and thus one has not advanced beyond belief. Kant’s distinction between the thing-in-itself and the phenomenon of consciousness is an instance of this absurdity. To make the distinction is to have the object in itself in consciousness and hence not in itself. Thus, Hegel concludes that knowledge and reality cannot be two things but must be identical. Knowledge cannot be perspectival or relative to each person; it is as absolute and objective as reality. Index Contemporary philosophy begins in the late 19th and early 20th century.
Much of what sets contemporary
philosophy off from modern philosophy is its explicit criticism of the modern
tradition and sometimes its apparent indifference to it. There are two basic strains of
contemporary philosophy: Continental philosophy, which designates the
philosophical style of western European philosophers, and Anglo-American, or
analytic, philosophy, which includes the work of many European philosophers who
immigrated to
In epistemology, Continental philosophers during the first quarter of the 20th century were preoccupied with the problem of overcoming the apparent gap between the knower and the known. If a human being has access only to his own ideas of the world and not the world itself, how can there be knowledge at all? The German philosopher Edmund Husserl (1859-1938) thought that the standard epistemological theories had become intrusive because philosophers were attending to repairing or complicating them rather than focusing on the phenomena of knowledge as humans experience them. To emphasize this reorientation of thinking, he adopted the slogan, “To the things themselves.” Philosophers needed to recover the sense of what is given in experience itself, and this could only be accomplished through a careful description of phenomena. Thus, Husserl called his philosophy “phenomenology,” which was to begin as a purely descriptive science and only later to ascend to a theoretical, or “transcendental,” science. Husserl thought that the philosophies of Descartes and Kant presupposed a gap between the aspiring knower and what is known and that the experience of the external world was thus dubious and had to be proven. These presuppositions violated Husserl’s belief that philosophy, as the most fundamental science, should be free of presuppositions. Thus, he held that it is illegitimate to assume there to be any problem of knowledge or of the external world prior to an investigation of the matter without any presuppositions. Husserl’s device to cut through the Gordian knot of such assumptions was to introduce an “epoché.” In other words, he would bracket or refuse to consider traditional philosophical problems until after the phenomenological description had been completed. The epoché was just one of a series of so-called transcendental reductions that Husserl proposed in order to ensure that he was not presupposing anything. One of these reductions supposedly gave one access to “the transcendental ego,” or “pure consciousness.” Although one might expect phenomenology then to describe the experience or contents of this ego, Husserl instead aimed at “eidetic reduction,” that is, the discovery of the essences of various sorts of ideas, such as redness, surface, or relation. All of these moves were part of Husserl’s desire to discover the one, perfect methodology for philosophy in order to ensure absolute certainty. Because Husserl’s transcendental ego seems very much like the Cartesian mind that thinks of a world but does not have either direct access to or certainty of it, Husserl tried in Cartesianische Meditationen (1931; “Cartesian Meditations”) to overcome the apparent gap the very thing he had set out either to destroy or bypass. Because the transcendental ego seems to be the only genuinely existent consciousness, Husserl also tried to overcome the problem of solipsism. Many of Husserl’s followers, including his most famous student, Martin Heidegger (1889–1976), recognized that something had goneradically wrong with the original direction of phenomenology. According to Heidegger’s diagnosis, the root of the problem was Husserl’s assumption that there is an “Archimedean point” for human knowledge, to use Husserl’s own phrase; but, there is no ego detached from the world and filled with ideas or representations, according to Heidegger. In Being and Time (1927) Heidegger returned to the original formulation of the phenomenological project as a return to the things themselves. Thus, all the transcendental reductions are abandoned. What he claimed to discover is that human beings are inherently world-bound. The world does not need to be derived; it is presupposed by human experience. In their prereflective experience, humans inhabit a sociocultural environment, in which the primordial kind of cognition is practical and communal, not theoretical or individual (“egoistic”). Human beings interact with the things of their everyday world (Lebenswelt) as a workman interacts with his tools; they hardly ever approach the world as a philosopher or scientist would. The theoretical knowledge of a philosopher is a derivative and specialized form of cognition, and the major mistake of epistemology from Descartes to Kant to Husserl was to take philosophical knowledge as the paradigm for all knowledge. Heidegger’s insistence that a human being is something that inhabits a world notwithstanding, he marked out human reality as ontologically special. He called this reality Dasein, the being, apart from all others, which is present to the world. Thus, like the transcendental ego, a cognitive being takes pride of place in Heidegger’s philosophy. In The epistemological views of Jean-Paul Sartre (1905-80) share some features with Merleau-Ponty’s. Both reject Husserl’s transcendental reductions, and both think of human reality as being-in-the-world. But Sartre’s views have Cartesian elements that were anathema to Merleau-Ponty. Sartre distinguished between two basic kinds of being. Being-in-itself (en soi) is the inert and determinate world of nonhuman existence. Over and against it is being-for-itself (pour soi), which is the pure consciousness that defines human reality. Later Continental philosophers attacked the entire philosophical tradition from Descartes to the 20th century for its explicit or implicit dualisms. Being/nonbeing, mind/body, knower/known, ego/world, being-in-itself/being-for-itself are all variations on a way of philosophizing that the philosophers of the last third of the 20th century have tried to undermine. The structuralist Michel Foucault (1926-84) wrote extensive historical studies, most notably The Archaeology of Knowledge (1969), in order to demonstrate that all concepts are historically conditioned and that many of the most important ones serve the political function of controlling people rather than any purely cognitive purpose. Jacques Derrida has claimed that all dualisms are value-laden but indefensible. His technique of “deconstruction” attempts to show that every philosophical dichotomy is incoherent, because whatever can be said about one term of the dichotomy can also be said of the other. Dissatisfaction with the Cartesian philosophical tradition can also be
found in the A.P. Martinich Index Analytic philosophy, the prevailing philosophy in the Anglo-American world in the 20th century, has its origins in symbolic logic on the one hand and in British empiricism on the other. Some of its important contributions have been nonepistemological in character, but in the area of epistemology its contributions have also been of the first order. Its main characteristics have been the avoidance of system building and a commitment to detailed, piecemeal analyses of specific issues. Within this tradition there have been two main approaches: a formal style, deriving from logic; and an approach emphasizing ordinary language. Among those who can be identified with the first method are Bertrand Russell, Gottlob Frege, Rudolf Carnap, Alfred Tarski, and W.V.O. Quine; and among those with the second are G.E. Moore, Gilbert Ryle, J.L. Austin, Norman Malcolm, P.F. Strawson, and Zeno Vendler. Wittgenstein can be situated in both groups, his early work belonging to the former tradition and his posthumous works, Philosophical Investigations (1953) and On Certainty (1969), to the latter. Perhaps the most distinctive feature of analytic philosophy is its emphasis upon the role that language plays in the creation and resolution of philosophical problems. These problems, it is said, arise through the misuses, oversimplifications, and unwarranted generalizations of everyday language. Wittgenstein said in this connection: “Philosophy is a battle against the bewitchment of the intelligence by means of language.” The idea that philosophical problems are in some important sense linguistic (or conceptual) is called the “linguistic turn.”
Commonsense philosophy, logical
positivism, and naturalized epistemology Three of the most notable achievements of analytic philosophy are
commonsense philosophy, logical positivism, and naturalized epistemology. G.E. Moore (1873-1958) made a defense of
what he called the commonsense view of the world. According to
The development of logical positivism (also called logical empiricism)
was a product of the W.V.O. Quine (b. 1908), in “Two Dogmas of Empiricism” (1950), launched an attack upon the notion that there is a difference in kind between analytic and synthetic statements. Quine argued powerfully that the so-called difference is one of degree. In a later work, Word and Object (1960), Quine developed a new type of philosophy, which he called “naturalized epistemology.” He rejected the notion that epistemology has a normative function and claimed that its only legitimate role is to describe the way knowledge is actually obtained. In effect, its function is to describe how present science arrives at the beliefs accepted by the scientific community. To a great extent the epistemological interests of analytic philosophers
in the 20th century have been concentrated upon the relationship between
knowledge and perception. The major
figures in this development have been Bertrand Russell, G.E. Moore, H.H. Price,
C.D. Broad, A.J. Ayer, and H.P. Grice. Although their views differed
considerably - Russell, Broad, and Ayer were phenomenalists, Grice was a
defender of the causal theory of perception, and
Sense-data theory was criticized by proponents of the so-called theory of appearing, such as G.A. Paul and W.H.F. Barnes, who claimed that the arguments for the existence of sense-data are spurious. Those arguments assume, for example, that because a penny looks elliptical from a certain perspective, it follows that there exists an elliptical object (sense-datum), which an observer is directly apprehending. They denied the inference, saying that the introduction of a separate entity, a sense-datum, does not follow from the fact that a circular object looks elliptical and to believe that it does is simply to misdescribe certain common perceptual situations. The most powerful attack on sense-data theory was generated by J.L. Austin in Sense and Sensibilia (1962). Many philosophers, in turn, rejected the theory of appearing. They felt that puzzles about the status of illusions and other visual anomalies still require explanation. Their aim was to give a coherent account of how knowledge is possible despite the existence of perceptual error. Realism and phenomenalism are the two main types of theories developed to account for these difficulties. Both realism and phenomenalism have had numerous variants. Two forms of realism, direct (naive) realism and representative realism (also called “the causal theory”), are historically important. Realism is both a metaphysical and an epistemological theory. The realist is committed to two principles: first, that some of the objects apprehended through perception are public and, second, that some of those objects are mind-independent. It is especially the second of these notions that distinguishes realists from phenomenalists. The realist believes that there is an intuitive commonsense distinction among various classes of entities perceived by human beings. One class consists, among others, of headaches, thoughts, pains, or desires, and the other of tables, rocks, planets, persons, animals, and certain physical phenomena such as rainbows, lightning, and shadows. The metaphysical aspect of realism sees the former as mental, the latter as physical. A realist metaphysics maintains that the classes are mutually exclusive. What a realist epistemology adds to this metaphysics is that mental entities are private, whereas physical objects are public. By “private” it is meant that each item belonging to the category of the mental is apprehensible by one person only. Thus, only one person can have a particular headache or a particular pain. In contrast, physical objects are public; more than one person can see or touch the same chair. The realist also believes that items belonging to the class of the physical are mind-independent. What is meant by this notion is that the existence of these objects does not depend upon their being perceived by anyone. Thus, whether or not a particular table is being seen or touched by someone has no effect upon its existence. Even if nobody is looking at it, it would still exist (other things being equal). But this is not true of mental phenomena. If somebody is not actually having a headache, realists would deny that the headache exists. A headache is thus mind-dependent in a way in which tables, rocks, and shadows are not. Realist theories of knowledge thus begin by assuming the public-private distinction, and most realists start by assuming that one does not have to prove the existence of mental phenomena. These are things of which each person is directly aware, and there is no special “problem” about their existence. But they do not assume this to be true of physical phenomena. As the existence of visual aberrations, illusions, and other anomalies shows, one cannot be sure that in any perceptual situation one is apprehending physical objects. All a person can be sure of is that he is aware of something, an appearance of some sort, say of a bent stick in water; but whether that appearance corresponds to anything actually existing in the external world is an open question. In the Foundations of Empirical Knowledge (1940) Ayer called this difficulty “the egocentric predicament.” When a person looks at what he thinks is a physical object, such as a chair, what he is directly apprehending is a certain visual appearance. But such an appearance seems to be private to that person; it seems to be something mental and not publicly accessible. What then justifies the individual’s belief in the existence of supposedly external objects - i.e., physical entities that exist external to the human mind? Direct realism and representative realism are the two main theoretical responses to this challenge. Both direct realism and representative realism rely strongly on sense-data theory. The technical term “sense-datum,” which played an important role in the development of versions of both theories, is sometimes explained by using examples. If one is hallucinating and sees pink rats, one is seeing a sense-datum. Although no real rats are there, one is having a certain visual sensation as of coloured rats, and this sensation is what is called a sense-datum. The image one sees with one’s eyes closed after looking fixedly at a bright light is another example. But, even in normal vision, one can be said to be apprehending sense-data. For instance, in looking at a round penny from a certain angle, one will see the penny to be elliptical. In such a case, there is an elliptical sense-datum in one’s visual field. This last example was held by Broad, Price, and Moore to be particularly important, for it makes a strong case for holding that one always sees sense-data, whether perception is normal or abnormal. According to defenders of sense-data theory, what these examples have in common is that in every perceptual act one is directly aware of something. A sense-datum is thus frequently defined as an entity that is the object of direct perception. By “direct” these philosophers mean that no inference is necessary in order to apprehend these entities. According to Broad, Price, and Ayer, sense-data differ from physical objects in having the properties they appear to have; i.e., they cannot appear to have properties they do not really have. The problem for a realist who accepts sense-data is to show how these private sensations allow justification of the intuitive belief that there are physical objects which exist outside of the individual’s perception. Russell in particular tried to show in such works as The Problems of Philosophy (1912) and Our Knowledge of the External World (1914) how knowledge of the external world could be built up from such mental, private apprehensions. During the 20th century direct realism took many forms; indeed there were
direct realists, such as James J. Gibson who, in The Ecological Approach to Visual
Perception (1979), rejected sense-data theory and claimed that the outside
aspects (the physical surfaces) of physical objects are normally directly
observed. But many realists, such
as G.E. Moore and his followers, believed that the existence of sense-data must
be accepted. All of these views have problems in dealing with perceptual anomalies.
In fact,
Because of the problems associated with direct realism, many philosophers, including H.H. Price, H.P. Grice, and Robert E. French, have argued for the causal theory, that is, the theory of representative realism. This is an old view whose most famous exponent in early modern philosophy was Locke. It is also sometimes called “the scientific theory” because it seems to be supported by findings in optics and physics. According to this form of realism there are real physical objects that exist external to the human mind, and there are also sense-data (or their equivalents, such as so-called mental representations). Visual perception is then explained as follows. Light is reflected from external objects, moves through space according to well-known laws of physics, is picked up by the human visual system, which includes the eye, the optic nerve, and the retina, and then is ultimately processed by the brain. This is a causal sequence. Light causes a reaction in the eye, that reaction is the cause of a response in the optic nerve, and so forth. The last event in this causal sequence is “seeing.” What one is apprehending in such a case is a mental representation (sense-datum) of the original object; and, through various processes in the brain, this representation gives human beings a depiction of the object as it is. Visual illusion is explained in various ways, but usually as the result of some anomaly in the causal chain that gives rise to distortions and other types of aberrant visual phenomena. In such a view, human observers are directly aware of mental representations, or sense-data, and only indirectly aware of the physical objects that cause these data in the brain. The difficulty with this view is that, since one cannot compare the sense-datum that is directly perceived with the original object, one cannot ever be sure that it gives an accurate representation of it; and therefore human beings cannot know that the real world corresponds to their perception of it. They are still confined within the circle of appearance after all. It thus seems that neither version of realism satisfactorily solves the problem it began with. In light of these difficulties with realist theories of perception some philosophers, so-called phenomenalists, proposed a completely different way of analyzing the relationship between perception and knowledge. In particular, they rejected the distinction between independently existing physical objects and mind-dependent sense-data that direct realism presupposes. They claimed that either the very notion of an independent existence is nonsense because human beings have no evidence for it or that what is meant by “independent existence” must be reinterpreted in such a way as not to go beyond the sort of perceptual evidence human beings do or could have for the existence of things. In effect, these philosophers challenged the cogency of the intuitive ideas that the ordinary person supposedly has about independent existence. All variants of phenomenalism are strongly verificationist in thrust. That is, they wish to maintain that belief in an external world must be capable of verification or confirmation, and this entails that such a belief cannot be acceptable if it goes beyond the realm of possible perceptual experience. Phenomenalists have thus tried to analyze in wholly perceptual terms what it means to say that any object, say a tomato, exists. They claim that any such analysis must start by deciding what is meant by a tomato. In their view a tomato is something that has certain properties, including a certain size, weight, colour, and shape. If one were to abstract the total set of such observed properties from the object, nothing would be left over; there would be no presumed Lockean “substratum” that supports these properties and which is itself unperceived. There is thus no evidence in favour of such an unperceivable feature, and no reference to it is needed in explaining what a tomato or any so-called physical object is. To talk about any existent object is thus to talk about a collection of perceivable features localized in a particular portion of space-time. Hence, what one means by a tomato is something that in principle must be perceivable. Accordingly, to say that a tomato exists is either to describe a collection of properties that an observer is actually perceiving or a collection that such an observer would perceive under certain specified conditions. To say, for instance, that a tomato exists in the next room is to say that, if one went to that room, one would see a familiar reddish shape, would obtain a certain taste if one bit into it, or would feel something soft and smooth if one touched it. To speak about that tomato’s existing unperceived in the next room thus does not entail that it is unperceivable. In principle, everything that exists is perceivable. Therefore, the notion of existing independently of perception has been misunderstood or mischaracterized by both philosophers and nonphilosophers. Once it is understood that objects are merely sets of properties and that such collections of properties are in principle always perceivable, the notion that there is some sort of unbridgeable gap between people’s perceptual evidence and the existence of an object is just a mistake, a confusion between the concepts of actually being perceived and of being perceivable. In this view, perceptual error is explained in terms of coherence and predictability. To say with truth that one is perceiving a tomato means that one’s present set of perceptual experiences and an unspecified set of future experiences will “cohere.” That is, if the object a person is looking at is a tomato, then he can expect that, if he touches, tastes, and smells it, he will receive a recognizable grouping of sensations. If the object he has in his visual field is hallucinatory, then there will be a lack of coherence between what he touches, tastes, and smells. He might see a red shape but not be able to touch or taste it. The theory is generalized to include what others would touch, see, and hear as well, so that what the realists call “public” will also be defined in terms of the coherence of perceptions. A so-called physical object is public if the perceptions of many persons cohere or agree, and otherwise it is not. This explains why a headache is not a public object. In similar fashion, a so-called physical object will be said to have an independent existence if the expectations of future perceptual experiences are borne out. If tomorrow, or the day after, a person has similar perceptual experiences to those he had today, then he can say that the object he is perceiving has an independent existence. The phenomenalist thus attempts to account for all the facts that the realist wishes to explain without positing the existence of anything that transcends possible experience. The criticisms of this view tend to be technical. Generally speaking, however, realists have objected to it on the ground that it is counterintuitive to think of a tomato as being a set of actual or possible perceptual experiences. The realist argues that human beings do have such experiences, or under certain circumstances would have them, because there is an object out there that exists independently of them and is their source. Phenomenalism, they contend, has the implication that, if no perceivers existed, then the world would contain no objects; and, if this is a consequence of the view, then it is surely inconsistent both with what ordinary persons believe and with the known scientific fact that all sorts of objects existed in the universe long before there were any perceivers. But its supporters deny that phenomenalism carries such an implication, and the debate about its merits remains unresolved.
Philosophy of mind and
epistemology In the late 1970s a series of developments occurred in a variety of intellectual fields that promise to cast new light on the nature of the human mind. There have been explosive advances in neuroscience, psychology, cognitive science, neurobiology, artificial intelligence, and computer studies. These have resulted in a new understanding of how seeing works, how the mind forms representations of the external world, how information is stored and retrieved, and the ways in which calculations, decision procedures, and other intellectual processes resemble and differ from the operations of sophisticated computers, especially those capable of parallel processing. The implications for epistemology of these developments are equally exciting. They promise to give philosophers new understandings of the relationship between common sense and theorizing, that is, whether some form of materialism which eliminates reference to mental phenomena is true or whether the mental-physical dualism which common sense assumes is irreducible, and they also open new avenues for dealing with the classical problem of other minds. It is too early to make an assessment of the relevance for epistemology of what has already been achieved in these areas. There is no doubt, however, that these advances are revolutionary and that a new area of intellectual discovery has begun. Avrum Stroll
Index The Competitiveness of Nations in a Global Knowledge-Based Economy January 2003
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