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Colour as a Secondary Quality by Paul Boghossian With J. David Velleman.

THE GALILEAN INTUITION Does modern science imply, contrary to the testimony of our eyes, that grass is not green? Galileo thought it did: Hence I think that these tastes, odors, colors, etc., on the side of the object in which they seem to exist, are nothing else than mere names, but hold their residence solely in the sensitive body; so that if the animal were removed, every such quality would be abolished and annihilated. Nevertheless, as soon as we have imposed names on them, particular and different from those of the other primary and real accidents, we induce ourselves to believe that they also exist just as truly and really as the latter. I The question whether Galileo was right on this score is not really a question about the content of modern scientific theory: aside from some difficulties concerning the interpretation of quantum mechanics, we know what properties are attributed to objects by physics. The question is rather about the correct understanding of colour concepts as they figure in visual experience: how do objects appear to be, when they appear to be green? Galileo seems to have found it very natural to say that the property an object appears to have, when it appears to have a certain colour, is an intrinsic qualitative property which, as science teaches us, it does not in fact possess. Subsequent philosophical theorizing about colour has tended to recoil from Galileo’s semantic intuition and from its attendant ascription of massive error to ordinary experience and thought. Thus, in a recent paper Sydney Shoemaker has written: [S]ince in fact we apply color predicates to physical objects and never to sensations, ideas, experiences, etc., the account of their semantics recommended by the Principle of Charity is one that makes them truly applicable to tomatoes and lemons rather than to sense experiences thereof. Should a principle of charity be applied in this way to the interpretation of the colour concepts exercised in visual experience? We think not. We shall argue, for one thing, that the grounds for applying a principle of charity are lacking in the case of colour concepts. More importantly, we shall argue that attempts at giving the experience of colour a charitable interpretation either fail to respect obvious features of that experience or fail to interpret it charitably, after all. Charity to visual experience is therefore no motive for resisting the natural, Galilean response to a scientific understanding of light and vision. The best interpretation of colour experience ends up convicting it of widespread and systematic error.3 CHARITABLE ACCOUNTS OF COLOUR EXPERIENCE According to the principle of charity, the properties that objects are seen as having, when they are seen as coloured, must be properties that they generally have when so perceived. Two familiar interpretations of visual experience satisfy this principle. The Physicalist Account The first of these interpretations begins with the assumption that what objects appear to have, when they look red, is the physical property that is normally detected or tracked by that experience. Since the physical property that normally causes an object to be seen as red is the property of having one out of a class of spectral-reflectance profiles-or one out of a class of molecular bases for such profiles-the upshot of the present interpretation is that seeing something as red is seeing it as reflecting incident light in one of such-and-such ways, or as having surface molecules with one of such-and-such electron configurations.4 Now, we have no doubt that experiences of an object as having a particular colour are normally correlated with that object’s possessing one of a class of spectral-reflectance profiles. But to concede the existence of such a correlation is not yet to concede that membership in a spectralreflectance class is the property that objects are seen as having when they are seen as having a particular colour. Indeed, the claim that visual experience has this content yields unacceptable consequences. In particular, this claim implies that one cannot tell just by looking at two objects whether they appear to have the same or different colours. For according to the physicalist interpretation, which colour one sees an object as having depends on which spectral-reflectance class one’s visual experience represents the object as belonging to; and which spectral-reflectance class one’s experience represents an object as belonging to depends on which spectral-reflectance profiles normally cause experiences of that sort. Hence in order to know whether two objects appear to have the same colour, under the physicalist interpretation, one must know whether one’s experiences of them are such as result from similar spectral-reflectance profiles. And the latter question cannot be settled on the basis of the visual experiences alone: it calls for considerable empirical enquiry. The physicalist interpretation therefore implies that knowing whether two objects appear to have the same colour requires knowing the results of empirical enquiry into the physical causes of visual experiences. But surely, one can tell whether two objects appear similarly coloured on the basis of visual experience alone. To be sure, one’s experience of the objects will not necessarily provide knowledge of the relation between their actual colours. But the physicalist account implies that visual experience of objects fails to provide epistemic access, not just to their actual colour similarities, but to their apparent colour similarities as well. And here the account must be mistaken. The apparent colours of objects can be compared without empirical enquiry into the physical causes of the objects’ visual appearances; and so the properties that objects appear to have, when they appear coloured, cannot be identified with the physical properties that are detected or tracked by those appearances. Dispositionalist Accounts We turn, then, to another class of theories that respect the principle of charity in application to colour experience. These theories are united under the name of dispositionalism. All of them are based, in one way or another, on the claim that the concept of colour is such as to yield a priori truths of the following form: (i) x is red if and only if x appears red under standard conditions.5 Different versions of dispositionalism interpret such biconditionals differently and apply them to the vindication of colour experience in different ways. Applying the Biconditionals: the Direct Approach Perhaps the most direct way to argue from the dispositionalist biconditionals to the veridicality of colour experience is to point out that the biconditionals assert, as a priori truths, that there are conditions under which things appear to have a colour if and only if they actually have it, and hence that there are conditions under which colour experience is veridical. The possibility of global error in colour experience is thus claimed to be excluded a priori by the very concept of colour. We think that this version of dispositionalism misappropriates whatever a priori truth there may be in the relevant biconditionals. We are prepared to admit that the concept of colour guarantees the existence of privileged conditions for viewing colours, conditions under which an observer’s colour experiences or colour judgements are in some sense authoritative. But colour experiences and colour judgements may enjoy many different kinds of authority, some of which would not entail that objects have the properties that colour experience represents them as having. Even philosophers who regard colour experience as globally false, for example, will nevertheless want to say that some colour experiences are correct in the sense that they yield the colour attributions that are generally accepted for the purposes of describing objects in public discourse. Of course, such a claim will yield slightly different biconditionals, of the following form: (ii) x is to be described as red if and only if x appears red under standard conditions. Our point, however, is that (ii) may be the only biconditional that is strictly true, and that (i) may seem true only because it is mistaken for (ii). If biconditional (ii) expresses the only genuine a priori truth in the vicinity, then the authority of experiences produced under standard conditions may consist in no more than there being a convention of describing objects in terms of the colours attributed to them in such experiences. As we shall argue at the end of this paper, such a convention may be perfectly justifiable even if all colour experience is, strictly speaking, false. Hence the intuitive support for biconditionals like (i) may not be such as to ground a vindication of colour experience. In order for the dispositionalist biconditionals to vindicate colour experience, they must mean, not just that convention dictates describing objects in terms of the colours that they appear to have under standard conditions, but also that objects actually have the properties that they thereby appear to have. And we see no reason for regarding this stronger claim as an a priori truth. Applying the Biconditionals as Content-specifications Another way of arguing from dispositionalist biconditionals to the veridicality of colour experience is to interpret the biconditionals as specifying the content of that experience. This argument proceeds as follows. The first premiss of the argument says that the property that objects are represented as having when they look red is just this: a disposition to look red under standard conditions. The second premiss says that many objects are in fact disposed to look red under standard conditions, and that these are the objects that are generally seen as red. These premisses yield the conclusion that the experience of red is generally veridical, since it represents an object as having a disposition that it probably has-namely, a disposition to look red under standard conditions. The first premiss of this argument corresponds to a biconditional of the following form: The right side of biconditional (iii) can be interpreted in two different ways, however; and so there are two different versions of the associated argument. Two Versions of Content-Dispositionalism The first version of the argument interprets the phrase a disposition to look red' on the assumption that the embedded phraseto look red’ has its usual semantic structure. The entire phrase is therefore taken to mean a disposition to give the visual appearance of being red'.6 The second version interprets the phrase on the assumption thatto look red’ has a somewhat unusual structure. The predicate following look' is interpreted as expressing, not a property that a thing is disposed to give the appearance of having, but rather an intrinsic property of the visual appearance that it is disposed to give. The phrasea disposition to look red’ is therefore taken to mean something like `a disposition to cause reddish visual appearances’.7 Under these two interpretations, (iii) assigns two different contents to colour experience. Under one interpretation, the property that things are seen as having when they look red is defined as a disposition to give the visual appearance of being red; under the other, the property that things are seen as having is defined as a disposition to cause reddish visual appearances. In either case, the content of colour experience is claimed to be true, on the grounds that objects seen as red do have the appropriate disposition. We regard both versions of the argument as faulty. In the next section, we shall raise an objection that militates against both versions equally. In subsequent sections, we shall consider each version in its own right. A General Problem in Content-dispositionalism Both versions of the present argument are to be faulted, in our opinion, for misdescribing the experience of colour. In assigning colour experience a dispositionalist content, they get the content of that experience wrong. When one enters a dark room and switches on a light, the colours of surrounding objects look as if they have been revealed, not as if they have been activated. That is, the dispelling of darkness looks like the drawing of a curtain from the colours of objects no less than from the objects themselves. If colours looked like dispositions, however, then they would seem to come on when illuminated, just as a lamp comes on when its switch is flipped. Turning on the light would seem, simultaneously, like turning on the colours; or perhaps it would seem like waking up the colours, just as it is seen to startle the cat. Conversely, when the light was extinguished, the colours would not look as if they were being concealed or shrouded in the ensuing darkness: rather, they would look as if they were becoming dormant, like the cat returning to sleep. But colours do not look like that; or not, at least, to us. More seriously, both versions of (iii) also have trouble describing the way in which colours figure in particular experiences, such as after-images. The colours that one sees when experiencing an after-image are precisely the qualities that one sees as belonging to external objects. When red spots float before one’s eyes, one sees the same colour quality that fire-hydrants and maraschino cherries normally appear to have.8 The problem is that dispositionalist accounts of colour experience must analyse the appearance of colour in after-images as the appearance of a disposition to look red under standard conditions; and after-images simply cannot appear to have such a dispositional property. This problem would not arise if after-images were full-blown illusions. That is, if seeing an after-image consisted in seeming to see a material object suspended in physical space, then that object, though in fact illusory, could still appear to have the same colour quality as any other material object. But after-images are not seen as material objects, any more than, say, a ringing in one’s ears is heard as a real noise. The items involved in these experiences are not perceived as existing independently of being perceived. On the one hand, the after-image is seen as located before one’s eyes, rather than in one’s mind, where visual memories are seen; and the ringing is likewise heard as located in one’s outer ear, rather than in the inner auditorium of verbal thought and musical memory. But on the other hand, one does not perceive these items as actually existing in the locations to which they are subjectively referred. The ringing is heard as overlaying a silence in one’s ears, where there is audibly nothing to hear; and similarly, the after-image is seen as overlaying the thin air before one’s eyes, where there is visibly nothing to see. The ringing is thus perceived as a figment or projection of one’s ears, the image as a figment or projection of one’s eyes: both, in short, are perceived as existing only in so far as one is perceiving them. Thus, the possibility of a red after-image requires that one see something as simultaneously a figment of one’s eyes and red. But how could something that looked like a figment of one’s eyes also appear disposed to look a particular way under standard conditions? Because an after-image is seen as the sort of thing that exists only in so far as one is seeing it, it cannot be seen as the sort of thing that others could see nor, indeed, as the sort of thing that one could see again oneself, in the requisite sense. In seeing an after-image as a figment of one’s eyes, one sees it as the sort of thing that will cease to exist when no longer seen and that will not be numerically identical to any future after-images, however similar they may be. One does not see it, in other words, as a persisting item that could be reintroduced into anyone’s visual experience; and so one cannot see it as having a disposition to present this or any appearance either to others or to oneself on other occasions. The foregoing, phenomenological problems are common to both versions of the dispositionalist argument currently under consideration. Each version of the argument also has peculiar problems of its own, which we shall now consider in turn. We begin with the first version, which understands a disposition to look red as a disposition to give the visual appearance of having the property red.