The traditional distinction between primary and secondary qualities has clear implications for the nature of perception. Primary qualities are possessed by objects independently of perceivers and do not owe their existence to perceivers: they are objective. Secondary qualities are dependent on perceivers, being projected by the mind onto objects that otherwise would lack them: they are subjective. Thus percepts have a subjective-objective duality: they are part subjective and part objective. For example, we see colors and shapes together, the former being contributed by the mind, the latter by the world outside the mind. These qualities become objects of perception by two different mechanisms: color qualities are manufactured by the mind and an operation of projection “spreads” them onto the physical world, while shape qualities impinge on the mind from outside and become perceptual contents by an operation of “imprinting” or “abstraction. Colors we impose on the world, while shapes impose themselves on us: from inside out and from outside in. Nevertheless the qualities interlock in a visual percept: we see color and shape simultaneously and side-by-side—we see colored shapes. Thus perceptual content is hybrid, double aspect, a mixture of opposites. We see both what comes from within and what comes from without. No doubt much of this is puzzling and problematic, even mysterious: how exactly does the projection operation work, and what is the process of abstraction? But it is commonly assumed that something like this dual picture must be true, given the prior distinction between primary and secondary qualities. Part of perception derives from the mind and part derives from the world, yet the two sources are miraculously combined into a unitary percept.
Not everyone agrees with this bipartite picture. The unreconstructed naïve realist will insist that all the qualities manifest in perception reflect external conditions of objects—including colors, sounds, tastes, smells. Nothing comes from us; everything enters the mind from outside. This theorist will resist the idea that perception involves any sort of error, as that objects seem to have colors they don’t really have. Perception is simply openness to a world that exists whether we exist or not. Color is as objective as shape. On the other hand, a Kantian will maintain that the content of perception is wholly subjective—it’s all like color considered as a secondary quality. Shape qualities derive as much from the mind as color qualities. Thus there is no perceptual duality: subjectivity applies across the board. Both positions cleave to homogeneity of perceptual content: all objective or all subjective. But the position sketched above rejects this homogeneity, holding that perception is essentially a joining of disparate qualities. Indeed, it is typically assumed that the mind cannot of its own devices produce shape content, and also that the world cannot produce color content. We have to wait for the world to create shape percepts in us, but we can (and must) proceed on our own when it comes to color, the world being impotent to produce color percepts.
The dual aspect picture suggests that our perceptual faculties first present a kind of bloodless sketch to us, which we then fill in by supplying qualities not present in it—like coloring in an outline. The primary qualities impinge on the mind and offer themselves for representation, but we have to complete the picture with appropriate secondary qualities. Of course, this process doesn’t involve any temporal separation between the initial sketch and the final coloring in, as if we had to wait for the colors to arrive, for we can make no sense of the idea of seeing shapes without accompanying colors (nor vice versa). But, logically speaking, there are two separate mental operations, of introjection and projection, respectively (maybe God can see objects without colors and can apply colors to objects at will). This is doubtless all very curious, but seemingly unavoidable, once we accept the picture of perception suggested by the traditional distinction. There must be some way in which subjective and objective qualities magically come together–coalesce, fuse– because we see both colors and shapes together, despite their being ontologically quite different. The inner and outer must be made to interlock in such a way that the unity of the percept is preserved.
It seems to me that the situation is sufficiently problematic that we should seek an alternative. I take it that the subjectivity of color is undeniable, so I reject the type of naïve realism mentioned above; but the Kantian line is worth pursuing. So let’s try out the following idea: the shape qualities we perceive are also products of the mind, derived from its own inner resources, just like color qualities. There are serious problems with the notion that we obtain ideas of shape by abstraction from experience; and there are reasons to suppose that the shapes we see are not the shapes exemplified in the objective physical world. I won’t say much about these points because they are well known; my question is whether adopting the Kantian line eases the problem of perceptual content—what we might call “the combination problem”. So, by way of reminder: it has been widely contended that the geometry of the physical world does not fit the perceptual geometry we naturally bring to it (non-Euclidian versus Euclidian, roughly), so the geometrical figures we perceive are not identical to those existing in objective reality. This is easy to accept for other species: we don’t suppose that the visual experience of a mouse or a snake correctly captures the true geometry of the material world. The mind (brain) invents its own geometry, geared to its biological requirements, and the corresponding qualities may be as subjectively constituted as color qualities. Secondly, some of the primary qualities we perceive simply don’t belong to the objective material world, so they must be contributed by the mind–for example, solidity and smoothness. Objects don’t have the kind of continuous structure they appear to, and they don’t have smooth edges. The world is more granular than it appears. We attribute these qualities to things in virtue of the perceptual apparatus we possess, so the mind (brain) must be generating the corresponding qualities: we see things as solid and smooth, and hence ascribe those qualities to things. We can’t extract these qualities from objects, since they don’t have them, so we must get them from somewhere else, namely from our own resources. There are also the well-known arguments from illusion: when you see a penny as elliptical the property you see is not present in the object, so it can’t derive from that object; it must come from within. The shape you see is not the shape the penny objectively has. In addition, perceptions of color must of necessity also be perceptions of shape, and colors are endogenously derived, so it makes sense that both should have the same source (what about hallucinations of red cubes before any cubes have been seen?). There seems every reason to believe that our perception of shape issues from an internal system that contains shape representations without reliance on an outside stimulus; and every reason to suppose that the qualities involved do not coincide with (are not identical with) the actual geometry of the physical world. The color system and the shape system are essentially connected, with both projected onto the world in a single package.
There are two things I am not saying here. One thing I am not saying is that the shape qualities we perceive are secondary qualities in the manner of color qualities, i.e. dispositions to cause experiences in perceivers. That looks like a false analysis in view of the non-relativity of attributions of shape. The qualities may be projected but they are not dispositional in this way (though they may be dispositional in other ways). The question of analysis is not the same as the question of origin or coincidence with objective traits of reality. Second, I am not saying that there is no systematic correspondence between perceived shape and objective shape. No doubt there is a close correspondence between them, given that perceivers have to live in a world of shaped objects and can’t afford to be completely wrong about their shapes. It is not that Euclidian and non-Euclidian geometry have nothing in common; in fact, they converge in many ways. The qualities we perceive act as surrogates for the objective traits of things, though the two are not identical. Just as colors correspond to wavelengths, so shapes (as perceived) correspond to the actual geometrical properties of things (which may come down to potentials in a force field). Objects certainly have edges, but the physical reality of edges need not coincide with edges as they are perceived.
Does this position deserve to be described as idealist? Yes and no. No, in that it doesn’t reduce reality to purely mental reality (there is a non-mental external world out there); and no, in that the shape qualities are not to be conceived as themselves mental (unlike experiences of them). But yes, in that the world we immediately perceive is a world of our own devising: its constituents (sensible qualities) derive from within the mind and are not found in objective reality. The world we immediately perceive is a projected world, much as Kant supposed. There are in fact two worlds: the phenomenal world of perception and the objective world that lies on the other side of perception. We can say that objects have the qualities we perceive them to have, but this is so only by dint of the (mysterious) mental act of projection—just as they have colors. It is just that objects don’t have these qualities independently of the minds that project them (unlike the qualities attributed by physics). We can even stick to a version of naïve realism, since we see non-mental qualities that objects have (albeit derivatively), not mental sense-data that intervene between the mind and non-mental reality. The mind has access to qualities (a type of universal) that it projects onto the world, but these qualities are not aspects of the mind—they are not sensations.
We should accordingly reject the old dichotomy of primary and secondary qualities in favor of a threefold distinction. There are the intrinsic properties of objective reality, the kind of thing talked about in physics (hopefully)—mass, charge, fields, etc. Then there are the properties that consist in dispositions to appear in certain ways—secondary qualities in the traditional sense. But third, there are properties like perceived shape that belong neither to objective reality nor to the class of dispositions to appear; these properties fit neither of the traditional categories. This third class is more closely interwoven with objective reality than the usual secondary qualities, which track nothing very significant in the external world (hence the non-relativity I mentioned earlier). The essential point is that perceived shape does not coincide with objective shape (and similarly for other so-called primary qualities like solidity, length, volume, etc.). The shapes (etc.) that we see are not the shapes that populate the objective universe. The class of properties traditionally counted as primary is thus more heterogeneous than was thought in the seventeenth century, when mechanism was still dominant and modern physics hadn’t questioned so much of common sense. It tended then to mean “any property of objects that is not secondary”. The possibility that the ontology of physics might be far removed from common perception was not really contemplated, so the assumption was that the way we see objects would figure in the correct science of those objects. It was Kant who began the movement to separate the phenomenal world from the objective world described by physics. The unexpected upshot is that we are now free to reject the double aspect theory of perceptual content, by regarding all such content as the product of the mind. We needn’t entertain the problematic idea of the subjective-objective amalgam.
Let me try to make the position vivid by imagining a toy world. In this world the geometry of reality is some radically non-Euclidian geometry that is not even capable of being perceptually represented by the creatures living there—perhaps it has 10 dimensions. The creatures nevertheless need a way to perceive their environment, so they invent (or their genes invent) a perceptual geometry that is psychologically manageable and succeeds in tracking external reality well enough to survive. The qualities denoted in this system are not found in objective reality, though they characterize how that reality is perceived. In this world (perceived) shape and color both originate in the mind, so there is no combining of the subjective and the objective, the endogenous and the exogenous. Then that is how it is in our world: we have constructed perceptual representations that serve our purposes but which don’t coincide with, or derive from, the objective features of things.