d before, and memory. Memory is not the process of forming an image of something one has experienced before. Condillac instead described it as the process of forming an idea just of signs or circumstances that have been associated with a previously experienced object. The operation of forming an image of a previously experienced object is not memory but “imagination,” or reminiscence, if the imagined object is thought of as one that has been experienced before. (Since signs are not discussed in the Treatise, the distinction between memory and imagination/reminiscence does not appear in that work, and both reminiscence and what the Essay calls vivid imagination are named “memory.” However, it is not clear that this is a doctrinal shift as opposed to a mere change of emphasis mandated by the different project of the Treatise.) Imagination becomes possible once a perception has become familiar from a number of previous experiences, which give the mind a facility to repeat that perception at will. The operation of imagination is enhanced if the perception is simple, composed of simple parts that are organized in accord with some guiding principle that can be invoked in reconstructing it, or customarily connected with other, presently occurring perceptions. Since connections with other, customarily connected perceptions need to be noticed, and attention is a function of need, which is in turn established by past experience of pleasure and pain, imagination is ultimately a function of past experience. The same can be said of memory, with the qualification that, insofar as memory involves the recollection of signs, its operation also presupposes the ability to make use of signs (Essay I.ii.2–3, Treatise I.ii).
Like Reid after him, Condillac drew a distinction between three kinds of signs: accidental, natural, and instituted (Essay I.ii.4).
Accidental signs are objects or circumstances that have been frequently encountered in conjunction with an object, so that the occurrence of the former induces the mind to imagine the latter. Though he made a great deal of the significance of his employment of the principle of association when giving summary presentations of his work, one of Condillac's great shortcomings is his treatment of association. He did little more than employ the term. Unlike Hume, he did not distinguish between resemblance, contiguity, and cause and effect, and he offered no detailed analysis of causal association. When compared with Hume's accounts of how association is responsible for our beliefs about matters of chance and probability, our trust in testimony, our reliance on general rules, and our tendencies to allow our reasoning to be influenced by credulity, education, and passion, Condillac's account of association is very impoverished.
Natural signs are the cries and gestures that we instinctively produce upon having particular experiences. Unlike Reid, Condillac insisted that we are not born with a knowledge of the meaning of natural signs; we are only born with the disposition to produce them on certain occasions. We produce them, moreover, without intending to do so and without intending to communicate anything by them. We only discover that they have a certain signification through hearing or seeing ourselves or others produce the sign on characteristic occasions, and so coming to associate the latter with the former. To go in the other direction, and produce the sign in order to induce the thought of some circumstance in others, would be to use the sign as an instituted rather than a natural sign.
The same might be said of accidental signs. To imagine dawn upon hearing the crow of a cock is to be affected by an accidental sign; to imitate the crow of a cock in order to signify dawn is to institute a sign, and is an operation of a higher order.
Reid was later to maintain that the creation of instituted signs presupposes an agreement among a community of speakers, which in turn presupposes language, and this led him to declare that there must be some language that is innately understood rather than establ