, necessarily experience itself as being two things at once, at least not if we take the term “thing” to refer to substances. Condillac claimed that, were each particular smell only ever experienced in conjunction with just one particular sound, and vice versa, the two would not be thought of as distinct things or substances, even though they would be distinguished from one another. Instead, the smell would be experienced as having a sound and the sound as having a scent. Otherwise put, each would play the role of property to the other. This is all that there ever is to our concept of substance, insofar as that concept has any meaning at all and is not simply a meaningless word invented by philosophers. Substance is not some substratum in which properties inhere, but a collection of sensations or qualities or properties commonly observed to occur together (Treatise I.xii.3, III.iv.2).
As has been noted, in the Treatise Condillac abandoned his earlier view that we immediately see depth. However, he continued to maintain that light and colours are extended over the remaining two dimensions. A being endowed with a sense of sight and presented with a variously coloured panorama would not experience all the different colours to be amalgamated into a point. Neither, Condillac supposed, would it blend the different colours with one another so as to see a uniformly coloured expanse. It would still continue to experience itself as simply being each of the colours it sees. Insofar as these colours are not merely multiple but outside of one another in space, the being would experience itself as not merely having a multiple existence, but also as being “outside” of itself. As Condillac put it, insofar as it is red it experiences itself as being outside of itself insofar as it is as green (Treatise I.xi.8).
It was at this point that Condillac's thesis that sensing does not entail being conscious of all that one senses came to the fore. We would think that if colours are extended and different colours are simultaneously seen without being blended, then there must be edges between them, and shapes outlined by those edges. Condillac accepted that this would in fact be the case. But he denied that his “statue” would necessarily have to be aware of this fact. The “statue” would need some reason to turn its attention to the boundaries between colours, to identify the various parts of those boundaries, and to notice what shape they constitute. But if it only considered colour sensations to be its own states of being, and took pleasure or pain only in their chromatic qualities and not in their shapes (a rather large presumption that Condillac seems not to have realized making), it would have no reason to notice that colours have shapes or even that they have particular locations relative to one another. Consequently, even though it would experience colours as being extended and outside of one another, it would not notice that the array of simultaneously present colour sensations forms an unbroken continuum. It would experience its coloured self merely as an aggregate of distinct extensions, vaguely perceived as not having any definite boundaries or shapes, and not recognized as having any locations relative to one another. Consequently, it would have no developed concept of space (Treatise I.xi.8–9).
Condillac maintained that it is only through the sense of touch that a being first acquires an awareness of space as an external continuum extending outwards beyond the bounds of its body, and an awareness of other objects in this space. Touch then teaches us to attribute smells, sounds, tastes, and colours to external objects.
Like Thomas Reid, who some ten years later also set about investigating what each of the senses can lead us to learn, Condillac took the tactile sensation of solidity to be crucial for the development of an awareness of space and of external objects. Only whereas Reid maintained that we are innately so constituted as to understand the purely qualitative sensation of solidity as sign signifying a quality of external object