As the average person understands the term experience, it means no more than familiarity with some matter of practical concern, based on repeated past acquaintance or performance. The experienced doctor or soldier knows his trade, not by the book merely, but by long practice under a variety of circumstances. The older philosophical meaning of the word differs but little from this, denoting as it does the capacity to do something, learned in the habit of doing it and guided rather by rule-of-thumb precept than by theoretical understanding (cf. the well-known passage in Aristotle, Posterior Analytics II, 19). It is in this fashion—by retention of individual memories and their gradual hardening into principle—that the craftsman acquires his skill, the scientist his knowledge, and the practical man his wisdom. But (save in the last case, perhaps) it represents at best only a stage on the way to real understanding...