Ridling Zaine. Philosophy: Then and Now. A look back at 26 centuries of thought

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Ridling, Philosophy Then and Now: A Look Back at 26 Centuries of Thought

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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

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,

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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.

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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 colored 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.

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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. Moore took the

unusual step of suggesting that such sense-data might not be mental entities

but could be a physical part of the surface of the perceived material object.

Thompson Clarke in “Perceiving Physical Objects and Surfaces” (1965) went

beyond Moore in arguing that one normally directly perceives the whole

physical object itself.

All of these views have problems in dealing with perceptual anomalies.

In fact, Moore, in his last published paper, “Visual Sense-Data” (1957),

abandoned the attempt to defend direct realism. He held that, because the

elliptical sense-datum one perceives when one looks at a round coin cannot be

identical with the circular surface of the coin, one cannot be seeing the coin

directly but only the sense-datum. Hence, one cannot have direct knowledge

of external objects.

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

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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.

Phenomenalism

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,

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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, color, 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 favor 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

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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

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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.

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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.

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Philosophy of Mind

Introduction

One attribute that sharply distinguishes man from the rest of nature is his

highly developed capacity for thought, feeling, and deliberate action. Here and

there in other animals, rudiments, approximations, and limited elements of

this capacity may occasionally be found; but the full-blown development that

is called a mind is unmatched elsewhere in nature.

The task assumed by the discipline known as the philosophy of mind is

to examine and analyze those concepts that involve the mind (including the

very concept of the mind itself) in an attempt to discover the nature of each of

these concepts, the relations between them, how they are to be classified, and

how they are to be related to certain other concepts – especially to the

concepts of matter and energy, the human body, and, in particular, the central

nervous system.

It should be clear that the range of topics in the philosophy of mind goes

far beyond what is intended in everyday discourse by “mind.” When, for

example, the layman speaks of someone as having “a good mind” or as

pursuing “the pleasures of the mind,” he is thinking of those particular

activities that have to do with abstract reasoning, intellectual pursuits, and the

exercise of intelligence. The “mind,” as the term is used more technically in

this article and in the philosophy of mind in general today, encompasses a

variety of elements including sensation and sense perception, feeling and

emotion, dreams, traits of character and personality, the unconscious, and the

volitional aspects of human life, as well as the more narrowly intellectual

phenomena, such as thought, memory, and belief.