"Technical knowledge, we have seen, is susceptible of formulation in rules, principles, directions, maxims - comprehensively, in propositions. It is possible to write down technical knowledge in a book. Consequently, it does not surprise us that when an artist writes about his art, he writes only about the technique of his art. This is so, not because he is ignorant of what may be called the aesthetic element, or thinks it unimportant, but because what he has to say about that he has said already (if he is a painter) in his pictures, and he knows no other way of saying it. And the same is true when a religious man writes about his religion or a cook about cookery. And it may be observed that this character of being susceptible of precise formulation gives to technical knowledge at least the appearance of certainty: it appears to be possible to be certain about a technique. On the other hand, it is a characteristic of practical knowledge that it is not susceptible of formulation of this kind. Its normal expression is in a customary or traditional way of doing things, or, simply, in practice. And this gives it the appearance of imprecision and consequently of uncertainty, of being a matter of opinion, of probability rather than truth. It is, indeed, a knowledge that is expressed in taste or connoisseurship, lacking rigidity and ready for the impress of the mind of the learner. Technical knowledge can be learned from a book; it can be learned in a correspondence course. Moreover, much of it can be learned by heart, repeated by rote, and applied mechanically: the logic of the syllogism is a technique of this kind. Technical knowledge, in short, can be both taught and learned in the simplest meanings of these words. On the other hand, practical knowledge can neither be taught nor learned, but only imparted and acquired. It exists only in practice, and the only way to acquire it is by apprenticeship to a master - not because the master can teach it (he cannot), but because it can be acquired only by continuous contact with one who is perpetually practising it. In the arts and in natural science what normally happens is that the pupil, in being taught and in learning the technique from his master, discovers himself to have acquired also another sort of knowledge than merely technical knowledge, without it ever having been precisely imparted and often without being able to say precisely what it is. Thus a pianist acquires artistry as well as technique, a chess-player style and insight into the game as well as a knowledge of the moves, and a scientist acquires (among other things) the sort of judgement which tells him when his technique is leading him astray and the connoisseurship which enables him to distinguish the profitable from the unprofitable directions to explore."