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Daniel Tarr

The Theory of Direct Realism

In the light of Theories of Perception

2001.

“If the doors of perception were cleansed everything would appear to man as it is: infinite.”
William BlakeThe Marriage of Heaven and Hell (1793)

INTRODUCTION

Realism in medieval philosophy meant that universals have real existence, meaning that general ideas have an ontological status too, just as the things they were abstracted from. There were two schools of realism. Extreme realism, represented by William of Champeaux, held that universals exist independently of both the human mind and particular things – a theory closely associated with that of Plato. Some other philosophers rejected this view for what can be termed moderate realism, which held that universals exist only in the mind of God, as patterns by which he creates particular things. St. Thomas Aquinas and John of Salisbury were proponents of moderate realism. In epistemology realism represents the theory that particular things exist independently of our perception. This position is in direct contrast to the theory of idealism, which holds that reality exists only in the mind. In modern philosophy, the term stands for a theory of knowledge according to which the world is full of independent objects and that it is these we perceive directly when we train our senses on them. This view of direct perception is also called direct or naïve realism. Most contemporary British and American philosophy tends toward realism. Prominent modern realists have included Bertrand Russell, G. E. Moore, and C. D. Broad. [1]

Direct or naïve realism is a theory of perception that holds that our ordinary perception of physical objects is direct, unmediated by awareness of subjective entities, and that, in normal perceptual conditions, these objects have the properties they appear to have. If a pickle tastes sour, the sun looks orange, and the water feels hot, then, if conditions are normal, the pickle is sour, the sun orange, and the water hot. Tastes, sounds, and colours are not in the heads of perceivers; they are qualities of the external objects that are perceived. Seeing an object is not – as representative theorists maintain – seeing it, so to speak, on mental television where the properties of a subjective sense-datum or percept (e.g. colour) represent or 'stand in for' the objective, scientific properties of the object (wavelength of reflected light). Although this theory bears the name 'naïve', and is often said to be the view of the person on the street, it need not deny or conflict with scientific accounts of perception. It need only deny that one's perceptual awareness of objective properties involves an awareness of the properties of subjective (mental) intermediaries. [2]

Perception is the sensory process enabling knowledge of the external world to be obtained. The philosophical problem of perception is epistemological: how to justify perceptual claims to knowledge? This question is not answered by psychology, which already assumes the existence of an external world. The main difficulty consists in showing why we should trust our perceptual experiences, given that we have apparently identical, but illusory, kinds of experience, such as dream and hallucination. [3]

Perception is of either things or facts. Seeing an object or an event, does not require that the object or event be identified or recognized in any particular way. One can see a cat on the sofa and mistake it for a rumpled sweater or see a man – in camouflage or at a distance, for instance – and take him for a tree. People have believed all manner of superstitious things about the eclipses they observed. Seeing objects and events is, in this sense, non-epistemic: one can see O without knowing or believing that it is O. Perceiving facts, on the other hand, is epistemic: one cannot see that there is a cat on the sofa without, thereby, coming to know that there is a cat on the sofa. Seeing a fact is coming to know (that this is a fact) in some visual way. Smelling a fact (e.g. that the toast is burning) is coming to know this fact in an olfactory way. In this way, then, thing-perception is cognitively less demanding than fact-perception. Both the dog and the cook can smell the burning toast (a thing), but unless it is a very smart dog (or a very dumb cook), only the cook will be able to smell, thereby coming to know (the fact), that the toast is burning. [4]

Factor of Perception

A great deal of perception (of both things and facts) is indirect. We perceive things on television, in the movies, and on records. One sees that the gas tank is empty by seeing not the gas tank, but the gas gauge and the fact that it reads 'empty'. This gives rise to questions about whether there are objects, and facts about those objects, that are seen directly. Direct realists believe that physical objects and certain facts about these objects are seen in some direct, unmediated fashion. One does not see the cup (nor the fact that it is a cup) by perceiving, in some more direct manner, an internal object (a cup-ish sense-datum) and certain facts about this datum (e.g. that it resembles a coffee-cup). [5]

Direct realism is opposed to a variety of views, grouped under the general term positivism [6] , according to which we perceive something else [7] : whether appearances, sense-data or some other intermediate entity that stands between us and the world. If this is true, then we have no direct perception of the independent objects, therefore we must remain skeptic about the reality of the external world; Berkeley's idealism questions whether objects exist when not experienced, while Hume questions whether objects exist at all beyond our experiences of them.

The sceptic view seems to be supported by the argument from illusion. Normally we see, feel, hear things as they are, but exceptionally our senses deceive us. We seem to see things that are not there, or things that appears otherwise than they are. The classical examples: that an oar seems to be broken when put into water [8] , or things look smaller when we move away from them, etc. are known to everybody. Since there are more than one examples to the argument from illusion, it is right to ask: what then is it that we see in such cases?

I. THE ARGUMENT FROM ILLUSION

Let’s start with the proposed problem, the argument from illusion: In some (if not most) cases of perception, we are aware of something that possesses different sensible properties from those possessed by the physical object we take ourselves to be perceiving. That of which we are aware is, therefore, something other than the object purportedly perceived. [9] This argument is in fact not one, but two arguments merged into one. The first argument is that if some of our experiences are illusory then we ought not to trust any of them. The second argument would say that only some of our experiences are illusory, and the real problem is in making the right judgment about which sensation to take as real. The first argument ignores the way in which we settle whether an experience is illusory or real. This ignorance comes from the difficult and highly criticized definition of what we call “experience”, which is the root of all misunderstanding. This approach to defining experience in this manner has such a deep root in the history of philosophy, that it seems sensible to retrace it’s major characteristics.

The problematic definition of experience:

According to Aristotle, having an experience of something, is not simply a matter of perceiving things; judgment and memory are needed, and experience is ‘with a view to action’ [10] . For Locke, on the other hand, having an experience of something may simply be a matter of having sensations; for sensation is the ‘great source of most of the ideas we have’ [11] . Locke’s concern is with experience as the source of ideas (as opposed to ideas being innate), not with experience (as opposed to knowledge of theory) as a guide to action. Both of Aristotle’s and Locke’s approach follow Plato’s, in imagining that our minds contain a block of wax which, when we perceive something, has an impression imprinted on it as a seal imprints something, an impression on wax [12] ; but they used this image differently. Aristotle, like Plato, used it in his account of memory. Memory is the persistence of the ‘sense-impression’ [13] . To explain sense-perception itself he used his notions of form and matter: a sense is ‘what has the power of receiving into itself the sensible forms of things without the matter’ [14] .

Locke used the image not only in his account of memory, but also in what he said about sense-perception. This led him to postulate, within sense-perception an element, sensation, in respect of which he is active; and to distinguish between them in terms of whether or not the perceiver can properly be said to be right or wrong: he cannot be if he only senses, he must be if he judges. Locke’s use, to explain perception itself, of the image of a seal imprinting an impression on wax, raises a question. How does the perceiver, given the sense-impression or sensation, arrive at a judgment? The answer is a development of the imprinting image. A seal may imprint words on wax in a foreign language. They have to be interpreted. Likewise, in perception, the perceiver ‘interprets’ the sensation. He interprets in the light of past experience, and judges accordingly. The act of interpretation takes place so quickly that he doesn’t notice it, and mistakes what is actually judgment for sensation [15] .

Unfortunately Locke’s introduction of sensations, as elements of perception not only made the definition of experience even harder, but gave a new ground to a whole new series of questions like: where can the sensations be located, and what is their cause, etc. We will have to come back to the problem of definition and location of sensations – these are the central topics of sense-data theories, [16] – but for now let’s try to get back to the main stream of thought.

It must be clear from this small survey, that the main difficulty is that sensation, judgment and experience is very hard to separate, when we have to apply these terms to perception. If we take the ‘two pencils’ example, it is hard to say what we exactly perceive. We have a sensation in our crossed fingers (it may be located elsewhere), which tells us that there are two pencils, but we have a second visual-sensation in our eyes which tells us the opposite. So if we want to know what we perceive, we have to make a judgment to construct our experience. This is, what is overlooked by the first argument of illusion: It is only by trusting some experiences that we can identify others as illusory. A pencil held between two crossed fingers feels like two pencils, yet we call this perception illusory. We only do this, because we trust our eyes better, than the feeling of there being two pencils between our crossed fingers. The problem from now is as follows: which experience should be regarded as real? Since it would be the most unnerving thing to think, that all of our experiences are illusory. Just because there are some perceptions which are illusory, we mustn’t conclude that they all are.

Therefore the first argument, which said that we mustn’t trust any of our experiences, is not necessarily true. If we believe that all of our experiences are illusory than we cannot come to the conclusion that there are illusory experiences. (Since we would lack the experience of real.) It is more likely that we must turn to the second argument from illusion, which would say that only some of our experiences are illusory, and the real problem is how we make the right judgment about deciding which sensations are illusionary or real.

The classic example of such an argument appears in the epistemology of perception; modern versions on the other hand focus on cases of total hallucination, where one seems to see something when there is nothing there at all, rather than on illusions such as the 'oar in water' case in which there is something there (the stick) which looks one way and is another. The argument, which is still called the argument from illusion, starts from the seemingly undeniable fact that it is impossible to distinguish (from the inside, as it were) a hallucination of being faced with an elephant from the state of actually being faced with an elephant. [17] What conclusion can we draw from this?

Suppose we hold that there are two states at issue here, a veridical one – which is a relation between perceiver and (external) object, and a hallucinatory one – which is a non-relational state of the perceiver. The argument from illusion then maintains that since there is no distinguishable difference between the two states, we must give a broadly similar account of them both. This suggests that the veridical state consists of two elements, one – the common element – which obtains even in hallucination, and the other – the presence of the outer object – which obtains only if we are lucky.

The argument is sometimes supposed to take us beyond this, and to support a particular account of the common element, the 'act-object' theory. The idea here is that since the deluded are not aware of outer things but are still aware of something, they must be aware of an inner thing (an appearance). We then appeal to the indistinguishability of hallucination and genuine perception to argue that in success too we are (primarily) aware of an appearance, sometimes called a 'percept', 'sensum', or 'sense-datum', and only secondarily aware of the outer object. But this move amounts more to an assertion of the act-object theory than an independent argument for it. For it assumes without argument that the content or nature of the hallucination is an inner object, when this was exactly what was in question. The adverbial theory, which denies that assumption, is equally compatible with the argument from illusion.

There is also a different, skeptical form of argument from illusion. This is just a special case of Cartesian skepticism. Descartes argued that we do not know that we are fully clothed, because we cannot distinguish the state of being clothed from that of being naked while dreaming that we are clothed. This is an argument from the general possibility of error; it argues from perceptual error to the conclusion that we never know that things are the way they look.

If that conclusion is intended to be entirely general, the premiss must be that there is no case at all in which we can distinguish our being right from our being wrong; all seemingly veridical states may for all we know be hallucinatory ones. This is a strong claim, and it is one which the first argument from illusion had no need to make. In attempting to support the 'common element'  theory, one need only suppose that in a reasonable range of cases we are unable to distinguish hallucination from genuine perception. [18]

Both of the arguments from illusion that we have considered so far concern perception. But their starting-point is one about indistinguishability. Considered in very general form, the argument from illusion argues from the indistinguishability of two states, one of which is a success and the other a failure, to what we might call the 'conjunctive thesis' that what one gets in success is a conjunction of two independent elements: (1) something which success and failure have in common and (2) something only present in successful cases.

If this is the general nature of arguments from illusion, there will be other examples to be found wherever there is indistinguishability. One such tries to persuade us that knowledge is some form of belief. You cannot tell (from the inside) whether your cognitive state is one of knowing or merely one of believing (truly or falsely, it doesn't matter which). Therefore, knowledge must be defined as belief plus something – e.g. as belief plus truth and justification, as in the tripartite definition of Gettier – also called the 'conjunctive' theory of knowledge – or the "perception as acquiring belief" definition of Armstrong. [19]

In these ways arguments from illusion have been a potent weapon in establishing a broadly Cartesian view of the mind.

II. THEORIES OF PERCEPTION

The argument from illusion points out the main difficulty of all the theories of perception, including the realistic approach. If we want to formulate an elementary theory, supported by the second argument from illusion, we will arrive at what is called the representative theory of perception – a theory maintaining that in ordinary perception one is directly, and most immediately, aware of subjective representations (sense-data, percepts, sensations) of the external world. Our knowledge of objective (mind-independent) reality is, thus, derived from (based on) knowledge of facts about one's own subjective experience – what we perceive is at best mere representations of things. [20]

Arguments for a representative theory of perception typically appeal to hallucinations and illusions, and thus referred to as the argument from hallucination: the contents of hallucinations are qualitatively similar to those of perceptual experiences. For example, seeing a white rabbit is the same from a subjective standpoint as hallucinating or dreaming of a white rabbit. The causes may be different, but the experiences are the same. Since in the case of hallucinations and dreams one is aware of a mental representation or image, it is reasonable to infer that in ordinary perception one is also aware of something subjective. The only difference between seeing a white rabbit (veridical perception) and hallucinating one is the cause of the sensation. In veridical perception, the effect (the internal image of which one is directly aware) represents the cause – the white rabbit – in some more or less accurate way. In the case of hallucination the cause – maybe drugs in the bloodstream – is misrepresented. [21]

Arguments appealing to the fallibility of one's knowledge of the external world have also been used to support a representative theory of perception: our knowledge of reality is based on a more certain (infallible) knowledge of the appearances – the internal representation – of reality. But even if this is, in some sense, true, it does not support a representative theory unless it is combined with the (questionable) premiss that knowledge of the appearances – that something looks red, for instance – requires an awareness of something that is red. This questionable premiss has been called the 'sense-datum fallacy'. If it is not assumed, the fact that our knowledge of the world's objects is based on their appearance does not imply that we are aware of anything other than the external objects themselves. [22]

Representative theorists also typically distinguish between primary and secondary qualities. Primary qualities are supposed to be the ones that are shared by the mental representation and the physical object it represents. The shape of an object, for instance, is represented by the shape of the visual image that results from our seeing that object. Colours and sounds, on the other hand, are secondary qualities: these are properties of the sensory experience that do not resemble the objective powers in objects that cause us to experience these qualities. The greenness of grass is in the perceiver, not in the grass. [23] Thus the argument from secondary qualities implies that physical objects do not possess secondary qualities intrinsically. As they are clearly possessed by that of which we are aware in perception, that of which we are aware in perception is not the physical object itself. The only plausible way to understand the relation between physical objects and secondary qualities is to think of the objects as possessing dispositions to produce the qualities in us properties of our sense-data. [24]

Behind the representative theory lie three philosophical assumptions: a) only judgments can be true or false; b) a person, to be justified, must have some basis for judging as he does; c) the basis must ultimately be something other than an other judgment. Therefore there must be an element that is not a judgment (and so not true or false). This might correspond to the stimulation of the sense organs, but must be mental (such that the perceiver is conscious of it) and the basis for the judgment the perceiver makes. This element is called a sensation or idea, and is said to ‘represent’ the external object, by ‘interpretation’. It provides the basis for the judgment, and suggests that there is an external object, with such-and-such qualities. Perception is accordingly defined as ‘the interpretation of sensations to yield knowledge of the external world’. That the external world exists, is postulated in the act of interpreting, and so knowledge of it is ‘mediated’ or ‘indirect’, while the perceiver is ‘immediately’ or ‘directly’ acquainted with the sensation.

I have given the definition of realism in the introduction to this paper, as the theory of direct perception of independent objects of an external reality. For A. J. Ayer perception is direct – normal perceptual judgements always go beyond experience which give rise to them because they embody common sense view of the physical world. The common-sense view is an acceptable theory with respect to the immediate data of perception. [25] This definition clearly contains one of the main realist theories of perception. If we want to formulate this simplest, and most widely accepted theory, we will arrive at the theory of direct realism [26] . This theory states, that we are directly aware of external objects. If we are to accept the validity of the second argument from illusion, – that the real problem is about right judgment about sensations – then we must question the possibility of direct perception. This is quite evident: if we were to perceive the objects as they are (directly), we would need to have the same experiences every time we come into contact with the same object. Since the second argument from illusion seems to be true, we have to say that we have no direct perception of the object. Directly, we only perceive sensations, which seem to give a description of the object. Unfortunately sensations seem to be under the influence of the circumstances of perception.

Holders of the first theory object to direct realism that for it perception cannot be causal, and misperceiving is impossible (this stands against the argument from illusion). Direct realists object to the representative theory, that they do not experience any interpreting of sensations, and that something not true or false cannot be a basis for something that is. Representationalists hold that knowledge claims should rest on what cannot be false. The active intellect can be right or wrong in interpreting the sensation, but in sensation itself the mind is a passive recipient of what comes to it from the external world. One can avoid having to choose between representationalism and direct realism, by denying that only judgments can be true or false. In a visual illusion the look of a thing is non-veridical. In the well-known Müller-Lyer figure one line looks longer than the other, but is not. [27]   This is not a matter of judgment. They still look unequal to someone who, knowing it to be an illusion, judges them to be equal. This provides no foothold for generalized skepticism. One cannot be aware of how something looks without being aware of the thing which he looks at.

However, this leaves open whether the external world exists at all. One might reply that the existence of material things is merely a hypothesis, or move on to phenomenalism; the view that material things are not anything over and above sensations. Phenomenalism is the doctrine that physical objects are reducible to sensory experiences, or that physical object statements can be analyzed in terms of phenomenal statements describing sensory experience. The main twentieth-century defenders of the view, A. J. Ayer and C. I. Lewis, tried, each in his own way [28] , to show how the content of a physical-object statement involves appeal to nothing more than sense-contents or sense-data, or anyhow sensory experience. R. Chisholm however showed that would not be possible to translate physical statements into phenomenal statements because phenomenal statements are dependent on physical descriptions of the observation conditions and conditions of the perceiver. [29]

Moreover, phenomenalists must invoke not only actual but also merely possible phenomena, possible experiences. However, the introduction of possible phenomena imports a complication, for the possibilities in question must be in some sense 'real' and not just logical. But real possibility is grounded in actual conditions. And what could function as the 'base' or 'ground' for the phenomenalist's actual conditions relative to which his possible phenomena are to be defined? What can ground such conditionals as: I would experience a sense-content of something white if I acted in a certain way? Presumably it would be just me and my properties (whether or not I myself am also to be reduced, as in neutral monism, or to be left standing as in Berkeley's subjective idealism). A major problem for such phenomenalism stems from perceptual relativity: white paper looks white under white light, red under red, etc. Any possible course of experience resulting from a possible course of action will apparently underdetermine our surroundings: it will determine, for example, that there is either white paper under red light or red paper under white light, or the like. For this reason among others, phenomenalism now has few defenders. [30]

What is general in every theory of perception, is that it uses sensations as it’s basis. Since both theories face the problem of judging what sensations are to be regarded as significant or real, we should try to give an exact definition of what can be understood under this term.

III. SENSATIONS AS ELEMENTS OF PERCEPTION

Before we do this, let’s try to give a further definition of what we may call perception, after the former analysis. When we say perception, we not only mean the sensation of what we perceive, but the understanding of that sensation. This understanding is based on the judgment of whether what we sense is real or illusory. If these two predicates are valid, then perception is the cognitive apprehension of something. The problem is, as we have pointed out in the second argument from illusion, is that this something is always a sensation; and it is a question of judgment how we understand it. Hallucination, being merely the apparent perception of something (which is not there (there = real)), cannot be discarded as not-perception, although it doesn’t have a real basis for it’s appearing sensations. It seems that the problem surmounts to what we define as sensations.

The problem of defining sensations

Descartes said that nature has told him, by his bodily sensations, that he was not present in his body merely as a pilot is present in a ship, but ‘as it were mixed up’ with his body, so that he and it formed a unity (Sixth Meditation). By his mind being ‘mixed up with’ his body he did not mean that his mind was in the parts of his body in which he had sensations. ‘Pain in the hand is not felt by the mind inasmuch as it is in the hand, but as it is in the brain’ [31] . That is, for a pain caused by the hand being squeezed to be felt in the hand a nervous impulse must reach the brain, with which the mind has connections via the pineal gland. The problem raised by Descartes is central: where should one locate sensations? For it is not clear at all. Lotze’s theory of “local sign”, tried to show that it is the mind, that locates bodily sensations, by understanding the local signs applied to them. [32] Unfortunately this isn’t necessarily true. As Oswald Külpe has pointed out, the experienced difference between a sensation in one’s right hand and one in one’s left can be simply one of the places in which it is felt, just as the experienced difference between sound heard as coming from one’s left can be simply one of the direction from which the sound is heard as coming. Like the explanation of the locating of sound-sources, the explanation of the locating of bodily sensations can be purely physiological. [33]

Whichever is the case, one can talk of having a sensation of something one is touching, such as the furriness and warmth of a cat. We may say that this involves having bodily sensations, in one’s fingers, which give one’s sensations their character. Normally one attends to the qualities of the object, but one can attend to the sensations in one’s fingers: one infers that the cat is furry and warm when touches it. This seems more plausible in the case of the warmth than in the case of the furriness, since warmth is a recognized bodily sensation. There is a difference of category between feeling the warmth of something with one’s finger, and one’s finger feeling warm. One’s fingers feeling warm is not a matter of feeling the warmth of one’s fingers with something (or if it is, we are not talking about a bodily sensation.)

The use of words like ‘warm’, refer to both qualities of objects and to bodily sensations. This double use of all our adjectives have already been noticed by Berkeley, when he argued against calling things warm (First Argument). According to him, being sentient, we can feel warm. To be right in calling objects warm we should have to be justified in ascribing to objects something like what we feel when we feel warm. But objects are non-sentient; so there is no basis for the ascription of warmth to objects. If we accept this then we should rather call sensations as something presented to the mind by our senses. If this is the case then we arrive at Locke’s theory of perception [34] , where perception is “the simple idea of reflection” and sensations are only elements in perception. These elements still need to be interpreted, but that is purely a question of judgment. A person cannot be said to be right or wrong in having a sensation, but can be said to be right or wrong in making a judgment.

Those who distinguish this way (like Locke or Descartes) sometimes accuse the ‘vulgar’ of mistaking a judgment for a sensation, particularly as regards the distance and three dimensionality of objects. Descartes says that the size, shape and distance of a staff ‘clearly depend upon the understanding alone’, but ‘are vulgarly assigned to sense’ because ‘custom makes us reason and judge so quickly’ that ‘we fail to distinguish the difference between these two operations and simple sense perceptions.’ [35]

This theory is certainly the source of the ‘sense-datum’ theory of perception propounded by Russell and Moore and others in the early part of the 20th century. [36] Accordingly a ‘sensation’ – as used by Locke – or a sense-data is a subjective entity (allegedly) having the properties the perceived external object (if there is one) appears to have. For example: in seeing a white circle under red light and at an oblique angle, the sense-datum would be red and elliptical (the way the white circle looks). According to sense-data theorists, one perceives an external object, a white circle, but what one senses (is acquainted with, directly apprehends) is a red ellipse: the subjective sense-datum. Then, if one is clever (and knows about the funny lighting), one infers, on the basis of the sense-data one directly apprehends, that there is (probably) a white circle causing the red, elliptical sense-datum. In this way our knowledge of sense-data is supposed to provide a foundation for all empirical knowledge. [37]

Of course this clearly reflects the positivist doctrine which holds that we must confine ourselves to what is ‘given’ to us in sense-experience as sources of knowledge. Now in this positivistic account, what is ‘given’ in sense-perceptions is the sense-datum. This is just a reformulation of the Locke’s mediator, the sensation. Since the positivistic approach is aware of the problem stated in the second argument from illusion, sense-datum is introduced along with the distinction between the mediated awareness of objects in the external world and immediate awareness of the sensation or sense-datum. The only novum in this theory, is whereas a sensation is by definition mental, a sense-datum might be independent from the mind. Moore, for example sought to introduce it by a sort of ostensive definition, a ‘picking out’ of an element in one’s experience of an object, an element that might continue to exist after the experience. [38]

IV. COGNITIVE APPEARANCE AS PERCEPTION

It seems, that Moore’s wishful thinking is some kind of formulation of the realist and positivist approach. What we call perception has to be more than mere presence of sensations; with the introduction of sense-datum, he tries to account for the cognitive apprehension, we defined in the beginning of the previous chapter. After having enumerated the problems around the term ‘sensation’, we have gained solid ground for saying, that perception consists of sensations, which are presented to the mind, and some kind of mental understanding, which is mainly the judging of sense-datum. This judgment, as we have shown, is about determining the nature of our sensation.

Having to decide when we may call a sensation real, and when can it be merely regarded as appearance or illusion, we have to give a definition of what is really ‘given’ to our senses as the external reality. To do this, we should look at a psychological approach to perception. The word ‘appearance’ is usually contrasted to ‘reality’, but in the following we will have to show, that the two meanings really refer to the same thing, and the ontological distinction between the two is just an interpretation of words. First of all we’ll have to make a distinction between two uses of the word ‘appearance’:

According to the first use of the term ‘appearance’, the shape (form) something appears to be to a given point of view is determined entirely by the laws of perspective. [39] Thus a round object, seen from a point of view at a certain angle to it’s surface, will present an elliptical appearance. Leibniz called this the ‘optical’ appearance. [40] To determine what optical appearance an object presents to a point of view it is not good enough to ask someone to occupies the point of view. He is almost certain to err on the side of the real shape he believes the object to be. Only if he erects a transparent screen at right angles to his line of vision of the object, and traces the objects outline on it, will he get its optical appearance right. [41] In the case of an illusion, such as that given by the Müller-Lyer figure [42] , lines which are the same length in the original will be the same length in the tracing (i.e. in the optical appearance). In an ambiguous figure, such as the one which can be seen as a duck looking in one direction or a rabbit looking in the other [43] , the same ambiguity will appear in the tracing as in the original.

In a quite different sense of ‘appears’, the lines in the Müller-Lyer figure will appear unequal in length, and the ambiguous figure will look to a perceiver either like a duck or like a rabbit. This double use of words seem to undermine every philosophical misunderstanding. The two senses of the use of ‘appearance’ can be traced in Reid’s writings [44] . He remarks on an artist’s need to acquire ‘the habit of distinguishing the appearance of objects to the eye, from the judgments we form by sight, of their color, distance magnitude and figure’. If we look at the sea from a cliff-top the ‘judgment we form by sight’ may be of a sea that is uniformly blue. To create this impression in the picture the artist must use a dark shade of blue for the near sea, a light shade for the far sea, and intermediate shades in between. To know what shade to use must attend to the sea in a manner that must be learnt and may be described as attending to the optical appearance. However, Reid is not writing about the optical appearance when he says that the masters in painting ‘know how to make objects appear to be the same color by making their picture really of different color’.

This is the second use of the term ‘appearance’. He is using the word ‘appear’ with the sense it has in the true proposition ‘the person who draws the Müller-Lyer figure knows how to make lines of equal length appear to be unequal’. How things appear, in this sense, normally determines what people judge themselves to be looking at. We add ‘normally’ to provide for the exceptional cases in which a person has reason to think that things are not as they appear. This sense of ‘appears’ may therefore be called the cognitive appearance (pertaining to knowledge).

There are four related conceptual differences between cognitive and optical appearances:

a) Cognitive appearances are subjective, whereas optical appearances are objective. The optical appearance of an object to a point of view is a function of the object’s real figure, color, and spatial position, but of nothing else. There would still be optical appearances of objects to points of view even if all sentient life ceased to exist. Cognitive appearance of objects appear to sentient beings that can recognize them.

b) If something cognitive appears to somebody, he must know that it does; if optically, he need not. Psychological experiments have shown, that even if somebody is trying to attend to the optical appearance he may get it wrong.

c) Something can cognitively appear to somebody only if he possesses the appropriate concept. For example: the duck-rabbit can look like a duck only to someone who knows what a duck looks like; not for optical appearances.

d) Cognitive appearances are related to their objects by being true or false of them. For example, the lines in the Müller-Lyer figure look unequal in length, but this appearance is non-veridical; really they are equal. Optical appearances are not true or false of the objects of which they are appearances: no more than the size of one angel of a triangle is true (or false) of the other two angels, which determine it’s size.

For an understanding of sense-perception as are means of knowing about the world it is the cognitive appearance that matters. This is wholly in accord with the current psychological approach according to which perception is really a hypothesis-making process.

V. SUMMARY

If we accept cognitive appearance as the basis of our sense-perception, then we cannot say that external objects are given to our perception either directly or in their full meaning. Therefore direct realism cannot be more than a naïve interpretation of what we perceive, that can only serve as a kind of ‘scientific method’ for a scientist in action.

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GLOSSARY

DIRECT or NAÏVE REALISM [See: Realism, Perception]

A theory of perception that holds that our ordinary perception of physical objects is direct, unmediated by awareness of subjective entities, and that, in normal perceptual conditions, these objects have the properties they appear to have. If a pickle tastes sour, the sun looks orange, and the water feels hot, then, if conditions are normal, the pickle is sour, the sun orange, and the water hot. Tastes, sounds, and colours are not in the heads of perceivers; they are qualities of the external objects that are perceived. Seeing an object is not (as representative theorists maintain) seeing it, so to speak, on mental television where the properties of a subjective sense-datum or percept (e.g. colour) represent or 'stand in for' the objective, scientific properties of the object (wavelength of reflected light). Although this theory bears the name 'naïve', and is often said to be the view of the person on the street, it need not deny or conflict with scientific accounts of perception. It need only deny that one's perceptual awareness of objective properties involves an awareness of the properties of subjective (mental) intermediaries.

Dretske, FredNaïve Realism in The Oxford Companion to Philosophy [© Oxford University Press 1995.]

EMPIRICISM [See: Phenomenalism]

In its strong form, the thesis that there is no reality behind appearances. Thus, it is the job of science to catalog the formal relations which hold between appearances without claims of describing reality. A weaker form of empiricism admits of the existence of a reality which is, however, trans-empirical. The transcendent nature of reality determines that we can have no knowledge of it and thus must simply catalog the formal relations between appearances. Empiricism is very much like phenomenalism. However, empiricism is a term more commonly used in philosophy of science than philosophy of mind. In either case, these positions are most commonly contrasted with realism.

Based on Eliasmith, Chris (ed.) – The Dictionary of Philosophy of Mind

IDEALISM: [See: Realism, Phenomenalism, Monism]

A brand of monism, first forwarded by Berkeley, in which everything is mental, as contrast to materialism. Idealism is a set of views according to which the physical world is dependent upon the mind; we somehow create the world. These doctrines are not as counter-intuitive as they seem because idealists are not saying that our experience of the world is other than it is, but that the explanation of our experience is other than we take it to be. So an idealist will not deny that tables and chairs are physical objects but he or she will give an account of what it is to be a physical object that makes the physical dependent upon the mental.

Based on the Oxford Paperback Encyclopedia [© Oxford University Press 1998.]

MATERIALISM

The philosophical view that reality – everything that actually exists – is material or physical. Materialism is therefore a form of monism. Many philosophers and scientists now use the terms `material' and `physical' interchangeably (distinct from physicalism). Characterized in this way, as a doctrine about what exists, materialism is an ontological, or a metaphysical, view; it is not just an epistemological view about how we know or just a semantic view about the meaning of terms. Materialism is rarely argued for directly, and is usually taken to be borne out by the success of the physical sciences. Hobbes may be cited as a modern proponent of materialism. For materialism to be true, minds or mental states must in some sense be identical with physical phenomena (presumably states of the brain or nervous system), a proposition which raises complex philosophical questions. A different sense of materialism is associated with Marx (dialectical materialism).

Based on the Oxford Paperback Encyclopedia [© Oxford University Press 1998.]

MONISM [See: Materialism, Idealism]

Monism is the thesis that all of reality is of one kind.In philosophy of mind, monism is usually contrasted with the dualist position that mind and matter are deeply different. Thus, monism is the claim that mind and matter essentially the same. However, this 'sameness' has come in a number of different and contradictory varieties. For example, Hobbes felt that the mental is merely and epiphenomena of the physical, thus the physical is the one real substance (Contemporary materialism is also a form of physicalistic monism (see Churchland, 1996). In direct contrast, Berkeley postulated that the physical is just a collection of ideas (hence, idealism) and thus the mental is the only thing that really exists. Finally, there are a number of positions similar to Spinoza's property dualism, often referred to as dual-aspect theory. Spinoza held a position in which the mental and the physical are simply two modes of a more basic substance (it should be noted that strictly speaking, Spinoza was not a property dualist as he held that the mental and the physical were two of a possible infinite number of modes of the basic substance, nevertheless he is typically labeled as one). For Spinoza, this basic substance was God. Thus the only real thing is God, who is neither physical nor mental. Spinoza's position is similar to that of Russell's NEUTRAL MONISM, – the doctrine that reality, though unified, is neither mental nor physical but rather conglomerations of a neutral entity –  however the latter is not committed to the belief that a supreme being is the more basic substance.

Based on Eliasmith, Chris (ed.) – The Dictionary of Philosophy of Mind

PERCEPTION

Perception is the sensory process enabling knowledge of the external world to be obtained. The philosophical problem of perception is epistemological: how to justify perceptual claims to knowledge? This question is not answered by psychology, which already assumes the existence of an external world. The main difficulty consists in showing why we should trust our perceptual experiences, given that we have apparently identical, but illusory, kinds of experience, such as dream and hallucination. Philosophical theories of perception include representational realism, which says that external objects are hypothesized in order to explain and match our experiences, and phenomenalism, according to which external objects are in fact nothing but bundles of experiences.

Perception is the extraction and use of information about one's environment (exteroception) and one's own body (proprioception). The external senses – sight, hearing, touch, smell, and taste – though overlapping to some extent, are distinguished primarily by the kind of information they convey (e.g. about light, pressure, sound, and temperature). Proprioception concerns stimuli arising and carrying information about, one's own body: acceleration, position and orientation of limbs, and so on.

Based on the Oxford Paperback Encyclopedia [© Oxford University Press 1998.]

PHENOMENALISM [See: Idealism, Monism, Representationalism]

The monistic view that all empirical statements – such as the laws of physics – can be placed in a one to one correspondence with statements about only the phenomenal (i.e. mental appearances). A view was held by A.J. Ayer but was shown by Roderick Chisholm to be untenable. Chisholm showed that would not be possible to translate physical statements into phenomenal statements because phenomenal statements are dependent on physical descriptions of the observation conditions and conditions of the perceiver.

The central idea of phenomenalism is well put in this passage from Poincare [1914, p. 14]:

     “[A] reality completely independent of the mind which conceives it, sees or feels it, is an impossibility. A world as exterior as that, even if it existed, would for us be forever inaccessible. But what we call objective reality is, in the last analysis, what is common to many thinking beings, and could be common to us all; this common part, we shall see, can only be the harmony expressed by mathematical laws. It is this harmony then which is the sole objective reality, the only truth we can obtain.”

Based on Eliasmith, Chris (ed.) – The Dictionary of Philosophy of Mind

PHILOSOPHY OF MIND

The branch of philosophy that is concerned with the nature of mental phenomena in general and the role of consciousness, sensation, perception, concepts, action, reasoning, intention, belief, memory, etc. in particular. Standard problems include those of free will, personal identity, mind-body problem, other minds, computationalism, etc. The philosophers of mind deal with metaphysics as it is concerned with the nature of mental phenomena, how mental phenomena are related to natural phenomena, and philosophical psychology broadly construed. Philosophy of psychology is sometimes considered as a subfield of philosophy of mind. However it is, perhaps, more closely related to philosophy of science.

In contrast to philosophy of psychology, philosophical psychology (and thus philosophy of mind) is concerned with investigations of folk psychology and focuses on discussions of such 'common sense' concepts as memory, sensation, perception, consciousness, belief, desire, intentions, action, reasoning, and so on. The more metaphysical problems include, first and foremost, the mind-body problem as well as the problems of free will, personal identity, and self-deception. Recently, much of the work in philosophy of mind has become closely associated to the interdisciplinary field of cognitive science. As cognitive scientists, philosophers of mind have become interested in a number of new problems including the relation between computation and thought, representations in the brain, and functionalism as it relates to minds.

Based on Eliasmith, Chris (ed.) – The Dictionary of Philosophy of Mind

POSITIVISM

Positivism is a movement akin to empiricism and naturalism and understood as the philosophical doctrine of Comte and his successors. It asserts that knowledge of reality can be achieved only through the particular sciences and ordinary observation. Positivism rejects all metaphysical propositions, but it has been pointed out (with regard to later logical positivism) that this rejection itself constitutes a metaphysical proposition. Hobbes was an earlier positivist with regard to the status of the law. The only law is positive law, the law that is actually enforced; there is no "higher" law such as natural law. Existentialism, especially in France, has been a reaction against positivism.

The Macmillan Encyclopedia 2001 [© Market House Books Ltd 2000.]

QUALITIES (PRIMARY AND SECONDARY)

Deriving from the Greek Atomists and common in the seventeenth century (Galileo, Descartes, Boyle) the distinction between these is famously found in Locke's Essay Concerning Human Understanding, where primary qualities (e.g. shape) are “utterly inseparable from ... [a] body”, however small [II. viii. 9.] and secondary qualities (e.g. colour) “in truth are nothing in ... objects themselves, but powers to produce various sensations in us” [II. viii. 10]. It is often supposed to be an epistemological doctrine concerning perceptual error and illusion, and so to depend on some idea that while we often err about the colours of objects we do not do so about their shapes, or that our perception of colour can vary with our position or with our mental and physical states. In fact, however, it is really a corollary of the corpuscular theory of matter, or, more generally, of the 'mechanical philosophy'.

Based on Woolhouse, RogerPrimary and Secondary Qualities in The Oxford Companion to Philosophy [© Oxford University Press 1995.]

REALISM [See: Direct Realism, Idealism, Phenomenalism]

Briefly, a realist about x holds that x enjoys mind-independent existence, that is, x exists regardless of whether anyone thinks, hopes or fears that x exists. It may sound odd to demand of minds and other things mental that they have mind independent existence, but the claim, for instance, that my mind is mind independent just means that I have a mind regardless of whether anyone thinks, hopes, or fears that I do. As well, a realist insists on there being explanations of the empirical world (including minds) in terms of the real world. Thus, a complete theory of the mind should explain the existence and functioning of minds in terms of the reality lying behind their empirically testable properties. This expectation strongly contrasts with the strictly empiricist position of phenomenalists.

In medieval philosophy realism represented a position taken on the problem of universals. There were two schools of realism. Extreme realism, represented by William of Champeaux, held that universals exist independently of both the human mind and particular things – a theory closely associated with that of Plato. Some other philosophers rejected this view for what can be termed moderate realism, which held that universals exist only in the mind of God, as patterns by which he creates particular things. St. Thomas Aquinas and John of Salisbury were proponents of moderate realism. In epistemology realism represents the theory that particular things exist independently of our perception. This position is in direct contrast to the theory of idealism, which holds that reality exists only in the mind. Most contemporary British and American philosophy tends toward realism. Prominent modern realists have included Bertrand Russell, G. E. Moore, and C. D. Broad.

Based on Eliasmith, Chris (ed.) – The Dictionary of Philosophy of Mind & The Columbia Encyclopedia [© 2001.]

REPRESENTATIVE THEORY OF PERCEPTION [See: Direct Realism]

A theory maintaining that in ordinary perception one is directly, and most immediately, aware of subjective representations (sense-data, percepts, sensations) of the external world. Our knowledge of objective (mind-independent) reality is, thus, derived from (based on) knowledge of facts about one's own subjective experience. Typically this view is contrasted with direct or naïve realism. The representative theory of perception remained part of the apparatus of empiricist thought, and is implicit in Hume's doctrine that what we are given is impressions, of which ideas are in some way copies. In the eighteenth century only Reid challenged the theory, because he thought it led Hume to absurdity. But the theory is still there in the thought of Kant, who held that perception provides us only with representations (Vorstellungen), however mediated by concepts. Kant held, however, that a mere subjective idealism (Berkeley’s) did not make it possible to distinguish properly what is objective from what is subjective in the sense in which flights of fancy are subjective.

Based on The Oxford Companion to Philosophy [© Oxford University Press 1995.]

SKEPTICISM

The philosophical the doctrine of skepticism is that real or true knowledge is unattainable. It is a general a skeptical attitude – doubting or critical disposition – in relation to accepted ideas, facts, etc. The ancient doctrine of skepticism (also called Pyrrhonism) was established by Pyrrho and continued at the Academy in Athens. In modern philosophy skepticism has taken many forms; the most extreme skeptics have doubted whether any knowledge at all of the external world is possible (solipsism): Descartes attempted to question his own existence; Berkeley's idealism asked whether objects exist when not experienced, while Hume questions whether objects exist at all beyond our experiences of them.

The Oxford English Reference Dictionary [© Oxford University Press 1996.]

SENSE-DATA

Subjective entities (allegedly) having the properties the perceived external object (if there is one)  appears to have. In seeing a white circle under red light and at an oblique angle, the sense-datum would be red and elliptical (the way the white circle looks). According to sense-data theorists, one perceives an external object, a white circle, but what one senses (is acquainted with, directly apprehends) is a red ellipse: the subjective sense-datum. Then, if one is clever (and knows about the funny lighting), one infers, on the basis of the sense-data one directly apprehends, that there is (probably) a white circle causing the red, elliptical sense-datum. In this way our knowledge of sense-data is supposed to provide a foundation for all empirical knowledge.

Based on Dretske, FredSense-Data in The Oxford Companion to Philosophy [© Oxford University Press 1995.]

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Bibliography

Primary Literature:

  • Berkeley, GeorgeTreatise concerning the Principles of Human Knowledge (1710) [Internet Encyclopedia of Philosophy © 1996]
  • Descartes, RenéMeditationes de Prima Philosophia (Meditations On First Philosophy) (1641) [translated by John Cottingham, Cambridge University Press, Cambridge 1996.]
  • Descartes, RenéPrinciples of Philosophy (1644) [translated by V.R. Miller and R.P. Miller, D. Reidel, Dordrecht 1983.]
  • Hume, DavidA Treatise of Human Nature (1740) [edited by L. A. Selby-Bigge, (2nd ed. revised by P.H. Nidditch), Clarendon Press, Oxford 1975.]
  • Hume, DavidEnquiries concerning Human Understanding (1748) [edited by L. A. Selby-Bigge, (3rd edition revised by P. H. Nidditch), Clarendon Press, Oxford 1975.]
  • Locke, JohnAn Essay Concerning Human Understanding (1690) [edited by Peter Nidditch’s Clarendon Press,  Oxford 1975.]
  • Reid, ThomasAn Inquiry Into the Human Mind on the Principles of Common Sense (1764) [Derek R. Brookes (ed.), Pennsylvania State University Press, University Park 1997.]

Secondary Literature:

  • Armstrong, D.M. Perception and Belief [from: A Materialist Theory of the Mind Humanities Press International Inc. and Routledge & Kegan Paul Ltd., NJ, 1968.]
  • Chisholm, Roderick Perceiving: A Philosophical Study [Ithaca, NY, 1957.]
  • Dretske, FredSeeing and Knowing [Chicago, 1969.]
  • Foster, JohnPerception [Oxford University Press, Oxford, 2000.] (Part 2.: "An Examination of Strong Direct Realism")
  • Moore, George EdwardHume’s Philosophy [Philosophical Studies, Kegan Paul, Trench, Trubner & Co. Ltd., London, 1922.]
  • Robinson, HowardPerception and Knowledge (Chapter VI.) [CEU – Empiricism Reader, 2001/2]
  • Russell, BertrandThe Problems of Philosophy (Chapter 1.) [New York, 1959]
  • Schlick, Moritz – "Positivism and Realism." {trans. David Rynin} [in Synthese 7. (1949)] (pp. 478-505.)
  • Strawson, P.F.Perception and its Objects [from: G. McDonald (ed.) – Perception and Identity (pp. 41-60.), Macmillan, London and Basingstoke, 1979.]

Internet Resources:

  • Xrefer – The Webs Reference Engine [© 2001 Xrefer.com] at {www.xrefer.com}
  • Fieser, James & Dowden, Bradley (eds.) – The Internet Encyclopedia of Philosophy [© 2001] at {http://www.utm.edu/research/iep/}
  • Dawson, Stephen (ed.) – The PAIDEA Project On-Line [American Organizing in the Paideia Papers Archive Committee, Inc. Boston University, 1996.] at {http://www.bu.edu/wcp/}
  • Zalta, Edward N. (ed.) – Stanford Encyclopedia of Philosophy [The Metaphysics Research Lab  Center for the Study of Language and Information, Ventura Hall, Stanford University] at {http://plato.stanford.edu}

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Footnotes

[1] Based on “Realism” in The Columbia Encyclopedia [© Sixth Edition, 2001.]

[2] Dretske, FredNaïve Realism in The Oxford Companion to Philosophy [© Oxford University Press 1995.]

[3] Based on “Perception” in the Oxford Paperback Encyclopedia [© Oxford University Press 1998.]

[4] See: Dretske, FredSeeing and Knowing [Chicago, 1969.]

[5] See: Chisholm, Roderick Perceiving: A Philosophical Study [Ithaca, NY, 1957.]

[6] This generalization is given in Moritz Schlick’s article: Positivism and Realism

[7] The representative theory of perception for example takes sense-data as the primary objects, and facts about sense-data as the basic facts, of perception.

[8] “Oar in water”: The favorite example of how circumstances can affect the perception of an object, and make it seem other than it is. 'The same object seems to us bent or straight, according to whether we see it in water or out of water' (Plato, Republic X. [602c]). Familiar in philosophy after Aristotle, the example divided skeptics (like Sextus Empiricus), who thought it showed that the senses give us no knowledge of an objective world, from Epicureans, who insisted that if there is mistake or ignorance in such cases, it must be attributed to the judgement, and not the senses (Lucretius, De rerum natura IV. 439 ff). Employed later by Descartes and Berkeley, the example was hackneyed enough by the time of Hume to count as one of the 'trite topics, employed by skeptics in all ages, against the evidence of sense'. It continued to feature in twentieth-century discussion, used, for example, by Ayer in support of a sense-datum theory of perception.

[9] Definition by Robinson, HowardArguments in the Philosophy of Perception [CEU – Empiricism, 2001/2]

[10] AristotleMetaphysics, Book 1. Chapter 1.

[11] Locke, JohnAn Essay Concerning Human Understanding (Book II. Chapter 1. / 3.)

[12] PlatoTheaetetus, 191c.

[13] AristotlePosterior Analytics, 99b 36.

[14] De Anima, 424 a 18.

[15] Locke, JohnAn Essay Concerning Human Understanding (Book II. Chapter 9. / 8-10.)

[16] See: Part III.: “Sensations as Elements of Perception”

[17] See: Part II.: “Theories of Perception” – The Argument from Hallucination

[18] Dancy, JonathanThe Argument from illusion in The Oxford Companion to Philosophy [© Oxford University Press 1995.]

[19] See: Armstrong, D.M. Perception and Belief [from: A Materialist Theory of the Mind, NJ, 1968.]

[20] The representative theory of perception remained part of the apparatus of empiricist thought, and is implicit in Hume's doctrine that what we are given is impressions, of which ideas are in some way copies. In the eighteenth century only Reid challenged the theory, because he thought it led Hume to absurdity. But the theory is still there in the thought of Kant, who held that perception provides us only with representations (Vorstellungen), however mediated by concepts. Kant held, however, that a mere subjective idealism (Berkeley’s) did not make it possible to distinguish properly what is objective from what is subjective in the sense in which flights of fancy are subjective.

[21] See: Robinson, HowardPerception and Knowledge (Chapter VI.) [CEU – Empiricism Reader, 2001/2]

[22] See: Dretske, FredThe Representative Theory of perception in The Oxford Companion to Philosophy [© Oxford University Press 1995.]

[23] Locke, JohnAn Essay Concerning Human Understanding (1690) Books II. and IV.

[24] Definition by Robinson, HowardArguments in the Philosophy of Perception [CEU – Empiricism, 2001/2]

[25] Ayer, A. J.The Central Questions of Philosophy (Chapters 4. and 5.) (pp. 68-111.) [London, 1973.]

[26] See: Strawson’s criticism and his distinction of “Confused (naïve) Realism” {Ayer}; “Scientific Realism” {Locke}; and “Common-sense Realism” {Mackie} in Strawson, P.F.Perception and its Objects

[27] See: Part IV.: “Cognitive Appearance as Perception” – first use of the term ‘appearance’

[28] See: Ayer, A. J.Language, Truth, and Logic [New York, 1952.] & Lewis, C. I.An Analysis of Knowledge and Valuation [La Salle, Ill., 1946.]

[29] See: Chisholm, R. M.'The Problem of Empiricism' [Journal of Philosophy (1948.)]

[30] Ernest, SosaPhenomenalism in The Oxford Companion to Philosophy [© Oxford University Press 1995.]

[31] Descartes, RenéPrinciples of Philosophy (IV. cxcvi.)

[32] See: Lotze, Rudolf HermannMikrokosmos (1856-1864); Lotze argued that nature, including life, can be explained mechanistically, but the unity of consciousness (our ability to compare two presentations and judge them (un)like) resists mechanical explanation. The causal interactions of nature presuppose that it is an organic unity of relatively permanent entities.

[33] See: The “Würzburg School” centered around Oswald Külpe, known for its experimental psychology of thinking

[34] Locke, JohnAn Essay Concerning Human Understanding (Book II. Chapter 9. – “Of Perception”)

[35] Descartes, RenéReply to Objections (VI. 9.)

[36] See: Russell, BertrandThe Problems of Philosophy (Chapter 1.) [New York, 1959]

[37] Dretske, FredSense-Data in The Oxford Companion to Philosophy [© Oxford University Press 1995.]

[38] See: Moore, G. E.Some Main Problems of Philosophy [London, 1953.]

[39] An “image” is an optical appearance or counterpart produced by light or other radiation from an object reflected in a mirror, refracted through a lens, etc.

[40] See: Leibniz, Gottfried WilhelmNew Essays on Human Understanding {a commentary on John Locke}

[41] This example can be found in  Atkinson et ali: Psychology, Ch. III.

[42] The Müller-Lyer illusion (1888), a well-established cognitive illusion whereby two lines of identical length appear to be of different lengths due to the addition of inward and outward facing arrowheads on the two lines, respectively.

[43] A visually ambiguous drawing, introduced by J. Jastrow. It can be perceived either as a duck or as a rabbit, but not both simultaneously. It exemplifies the concept-laden character of some forms of perception, and provides a connecting link to examination of the perception of speech and writing. The “duck-rabbit” example constitutes the starting-point for Wittgenstein's study, in Philosophical Investigations, ii. ix, of “aspect perception”. Wittgenstein showed an interest in the phenomenon to which the Gestalt psychologists had drawn attention, of seeing (or hearing) something as something. Part of Wittgenstein's interest in this phenomenon had to do with his rejection of a naïve account of perception; he took the interpretation of what is seen to be less separable from seeing itself than empiricist philosophers had been wont to think…

[44] Inquiry into the Human Mind, VI. 3.

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