say, he specified that there is nothing in bodies that resembles colours or scents and that these qualities are something that belongs to sentient creatures alone (Essay I.i.2. §12). In the Treatise, employing a striking turn of phrase, he claimed that while we might think of a being who possessed only the sense of smell as a being who scents a rose, for itself this being will simply be the smell of a rose. “From its perspective,” he wrote, “the odours are nothing other than its own modifications or manners of being” (Treatise I.i.2). The same holds of colours. A being whom we would describe as seeing red would at first experience itself as simply being red. Touch would instruct it to attribute this redness to other objects. But this instruction cannot be known to be correct, whereas there can be no question that the sensation of red is a modification of the being of a sentient creature. Red is not, therefore, what might be called the intentional object of an act of sensing, or if it is, it is so only derivatively; it is primarily a quality of the sentient being, who experiences itself as literally turning red when it has this sensation (Treatise I.xi.8).
The problem with this position becomes clear when it is considered that Condillac also maintained that colours are extended. In the Essay he claimed that were we to have no other sensations than those of light and colour they would “trace (traceront) extension, lines, and figures before our eyes” so that we would find these ideas to be contained in our sensations (Essay I.i.2. §9). Moreover, this discovery is not an effect of learning or association. Extension and shape are original features possessed by visual sensations, discernible simply by attentive reflection. Someone blind since birth and newly made to see would not originally perceive everything before him as if it were a “point” (i.e., an unextended spot of colour), but would experience “light distributed (répandue) in every direction [outwards as well as above, below, to the left and to the right]” (Essay I.vi. §§12, 14). Condillac continued to retain this view in the Treatise, though with some refinements: Whereas in the Essay he had maintained that colours are extended over all three dimensions, in the Treatise he endorsed the Berkeleyan position that we learn to perceive depth. He also maintained that we do not immediately appreciate that colours are bounded and figured even in two dimensions, but need to learn that they have these features. But he continued to maintain that the colours we originally experience are extended over two dimensions. “Colour presents [offre] extension to the soul that it modifies,” he wrote in the Treatise, “because it is itself extended. This is a fact that cannot be brought into doubt. It is demonstrated by observation” (Treatise I.xi.8). Insofar as colours are extended they must have shapes, even if those shapes are not immediately perceived. The process of learning to perceive shape does not transform our colour sensations and lead them to acquire properties they did not previously have; it merely leads us to discover ones that were there all along. This is the point of claiming that not everything that is necessarily involved with a sensation need be perceived by it.
Condillac thus appears to have been committed to four mutually antagonistic propositions:
- Colours are extended.
- Colours are sensations.
- Sensations are modifications of the mind's being.
- The mind is unextended.
Hume had confronted the conflict between these propositions by denying (3) and (4). For Hume, our visual impressions are compounds that consist of a number of minimally visible, coloured points that are disposed alongside another in space, but the notion that impressions and ideas inhere in some mental substance is unintelligible, whether this substance is taken to be material or immaterial. Reid, in contrast, had insisted on (3) and (4) but had declared that the term “colour” is used equivocally in (1) and (2). We experience sensations of colour, which are unextended states of feeling experienced 