 In the Essay, Condillac distinguished between reminiscence, understood as the perception that one is perceiving something that one has perceived 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).