Suppose that the organism is given the problem of determining the analysis of a stimulus at a certain level of representation- e.g., the problem of determining which sequence of words a given utterance encodes. Since, in the general case, transducer outputs underdetermine perceptual analyses, we can think of the solution of such problems as involving processes of non-demonstrative inference. In particular, we can think of each input system as a computational mechanism which projects and confirms a certain class of hypotheses on the basis of a certain body of data.