The need of going back of Aristotle in our quest for the truth is well shown by his attitude toward the first principles of the several sciences. To him they are immediately given--[Greek: amesoi protaseis]--and hence are ultimate _a priori_. The historical significance of this fact is already apparent. It means that in his day these first principles, which sum up the outcome of previous inductive movements of thought, were regarded as so conclusively established that the steps by which they had been inferred were allowed to lapse from memory. No account of the history of thought can hope to satisfy the demands of reason that does not _explain_ the origin of the convictions thus embodied in principles. The only acceptable explanation would be in terms of will and interest. To give such an account would, however, require the knowledge of secular pursuits and ambitions no longer obtainable. It might be fruitful of results if we could discover even the theoretical interests of the age before Thales; but we know that in modern times the direction of interest characteristic of the purely practical pursuits manifests its reformative influences in speculation a century or more after it has begun to shape the course of common life. Hence we might misinterpret the historical data if they were obtainable. But general considerations, which we need not now rehearse, as well as indications contained in the later history of thought, hereinafter sketched, point to the primacy of the practical as yielding the direction of interest that determines the course it shall take. It was said above that the principles of science are the result of an inductive movement, and that the inductive movement is directed by an interest. Hence the principles are contained in, or rather are the express definition of, the interest that gave them birth. In other words, there is implied in all induction a process of deduction. Every stream of thought embraces not only the main current, but also an eddy, which here and there re-enters it. And this is one way of explaining the phenomenon which has long engaged the thought of philosophers, namely, the fact of successful anticipations of the discoveries of science or, more generally still, the possibility of synthetic judgments _a priori_. The solution of the problem is ultimately contained in its statement.[88]