 and its role both in the acquisition of our more sophisticated cognitive powers and in the generation of false philosophies. These are topics that Condillac later relegated to his works on logic.
In the Treatise Condillac focused just on our pre-linguistic cognitive abilities, which he came to think he might have underestimated when he wrote the Essay. He retracted his earlier claim that perception is a transparent process and accepted both that it involves unconscious inference from what is given in sensation and that sensation itself may contain more than it is at first perceived to contain. He also retracted his earlier claim that depth is immediately perceived by vision. To support these revised opinions, he proposed a famous thought experiment. He asked his readers to consider an originally inanimate and insentient human being (Condillac spoke of a being that is just a “statue” of a human being) and to consider what this being could come to know were it to acquire each of the senses in isolation from the others, or each in combination with just one or two others. In proposing this question Condillac was asking a more radical version of the question Molyneux had posed to Locke: would a person born blind and made to see perceive spatial features well enough upon first sight to be able to identify cubes and spheres without touching them? Condillac was asking what a person endowed with just a sense of smell would think upon acquiring the power of hearing, or what a person endowed with vision would know if unaffected by hunger, incapable of motion, and unaware of any tactile sensation. His answer to these questions sought not just to explain how this person would acquire ideas of space and of external objects, but to prove that nothing more would be needed for it to acquire all the knowledge and all of the abilities that we have other than just to experience a sufficiently rich array of sensations.
Condillac's other philosophical works support and embellish the doctrines of the Essay and the Treatise. They are the Treatise on Systems of 1749, which is devoted to critiquing the metaphysics and the methodology of earlier philosophers, the Treatise on Animals of 1755, which attempts to explain how human souls differ from those of animals with respect to intelligence and free will, the “Dissertation on Liberty”, an important short work appended to the Treatise on Sensations that further addresses the issue of human free will, the “Summary [extrait raisonné] of the Treatise on Sensations,” originally included in the Treatise on Animals, and a textbook on Logic (1780). He also published a work on commerce and government, assembled a dictionary of synonyms, and put together a multi-volume course of studies that he had developed while tutoring the Prince of Parma. The latter dealt principally with history but also included some philosophical material, including a different presentation of logic. At the time of his death he left an incomplete a work entitled The Language of Calculation.
Condillac's account of the development of our cognitive capacities was informed by a particular conception of the nature of the mind and the sensations it is originally given. He argued that the mind must be an unextended or immaterial substance (Essay I.i.1 §6). When it senses, nothing actually passes into it from the outside world or the body. Instead the action of external objects on the sense organs brings about changes in the body and these changes serve as the merely occasional cause of the production of sensations in the mind.
Sensations are modifications of our being. To understand them as images of something distinct from us is to treat them as “ideas” rather than simply as “sensations,” and that is an operation that is so far from being automatic that it exceeds the capacities of animals. However, unlike Reid, who was later to argue for a rigorous distinction between sensations, considered as states of feeling experienced by the mind, and perceptions, considered as acts of thinking something about an object, Condillac maintained that se