Thus a history of psychology could be written by taking “completed” systems, analyzing the functional equivalence of the categories applied, and reducing every new system to a collection of synonyms for the terms of preceding systems. This hypothetical history of psychological theories would show how an inquirer, much impressed by certain experiences, would seize upon certain terms to describe them, and how, confronted by more and more empirical realities, he would modify the distinctive meaning of his explanatory conceptions out of existence. A history of psychoanalytic terminology, such as Rank has sketched in his treatment of genetic psychology, might be raw material for such a comparison. Would nothing remain but dictionaries of synonyms, all rather dubious contributions to the grist of linguistic research? It might be that our projected history would show that each psychological system left a permanent legacy behind it in the form of a significant “mechanism” which had not previously been stressed. Now the whole world of “causation” is implicated in any event, and the whole number of significant mechanisms which may be discerned in the “mind at a moment” is infinite. So our hypothetical volume might conclude by accepting the assumption that some events can be brought about by more than chance frequency, subject to the reservation that experimental confirmation is never reliable as to the future. The critical configurations may never “reappear.” We commonly say that the probability of an event’s future repetition is greater if it has been oft repeated in the past. But there is no means of demonstrating that the future contains analogous configurations to the elapsed. The probability of the future repetition of an event is “no probability.” If events appear to be predictable, this is so because our knowledge of contingencies is limited, and our sequences of similar configurations may still be treated as special instances of “no sequence.” The stable is a special case of the unstable, to put the ultimate paradox. The discovery of aggregates of mechanisms whose rearrangement in short periods would enrich the apparatus of social control is the dream (the mirage?) of psychology. Whether these objections will be well founded depends on the outcome of the test, and are incapable of dialectical resolution. It may be pointed out that the search for generalized mechanisms rests on no firmer logical foundations than the search for subjective sequences, since mechanisms are likewise aspects of the world of events, and as such are subject to the same “no probability” laws of recurrence.