 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).[1]  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. 