The proficient performer, immersed in the world of his skillful activity, sees what needs to be done, but must decide how to do it. The expert not only sees what needs to be achieved; thanks to a vast repertoire of situational discriminations he sees how to achieve his goal. The ability to make more subtle and refined discriminations is what distinguishes the expert from the proficient performer. The expert has learned to distinguish among many situations, all seen as similar by the proficient preformer, those situations requiring one action from those demanding another. That is, with enough experience in a variety of situations, all seen from the same perspective but requiring different tactical decisions, the brain of the expert performer gradually decomposes this class of situations into subclasses, each of which shares the same action. This allows the immediate intuitive situational response that is characteristic of expertise.

The expert chess player, classed as an international master or grandmaster, experiences a compelling sense of the issue and the best move. Excellent chess players can play at the rate of 5 to 10 seconds a move and even faster without any serious degradation in performance. At this speed they must depend almost entirely on intuition and hardly at all on analysis and comparison of alternatives.

[A few years ago Stuart performed an experiment in which an international master, Julio Kaplan, was required to add numbers presented to him audibly at the rate of about one number per second as rapidly as he could, while at the same time playing five-second-a-move chess against a slightly weaker, but master level player. Even with his analytical mind completely occupied by adding numbers, Kaplan more than held his own against the master in a series of games. Deprived of the time necessary to see problems or construct plans, Kaplan still produced fluid and coordinated play.

Kaplan's performance seems somewhat less amazing when one realizes that a chess position is as meaningful, interesting, and important to a professional chess player as a face in a receiving line is to a professional politician. Almost anyone can add numbers and simultaneously recognize and respond to faces, even though each face will never exactly match the same face seen previously, and politicians can recognize thousands of faces, just as Julio Kaplan can recognize thousands of chess positions similar to ones previously encountered. The number of classes of discriminable situations, built up on the basis of experience, must be immense.] It has been estimated that a master chess player can distinguish roughly 50,000 types of positions.

Driving probably involves the ability to discriminate a similar number of typical situations. The expert driver not only feels when slowing down on an off ramp is required; he simply performs the appropriate action. What must be done, simply is done.

We can see now that a beginner calculates using rules and facts just like a heuristically programmed computer, but that with talent and a great deal of involved experience, the beginner develops into an expert who intuitively sees what to do without recourse to rules. The tradition has given an accurate description of the beginner and of the expert facing an unfamiliar situation, but normally an expert does not calculate. He does not solve problems. He does not even think. He just does what normally works and, of course, it normally works.

The description of skill acquisition I have presented enables us to understand why the knowledge engineers from Socrates, [to Samuel], to Feigenbaum have had such trouble getting the expert to articulate the rules he is using. The expert is simply not following any rules! He is doing just what Socrates and Feigenbaum feared he might be doing -- discriminating thousands of special cases.

This in turn explains why expert systems are never as good as experts. If one asks an expert for the rules he is using one will, in effect, force the expert to regress to the level of a beginner and state the rules he learned in school. Thus, instead of using rules he no longer remembers, as the knowledge engineers suppose, the expert is forced to remember rules he no longer uses. If one programs these rules into a computer, one can use the speed and accuracy of the computer and its ability to store and access millions of facts to outdo a human beginner using the same rules. But such systems are at best competent. no amount of rules and facts can capture the knowledge an expert has when he has stored his experience of the actual outcomes of tens of thousands of situations.

[This in turn explains the common sense knowledge problem. The basis of common sense is our skill for coping with everyday materials. It is a knowing-how, not as knowing-that. (Example common sense physics. Children play with water for years building up the necessary thousands of typical cases.) This would explain why research in AI has been stalled and why we should expect the attempt to make intelligent computers by using rules and features to be abandoned by the end of this century.] [In this idealized account of skillful expert coping it might seem that experts needn't think and are always right. Such, of course, is not the case. While most expert performance is ongoing and nonreflective, the best of experts, when time permits, think before they act. Normally, however, they don't think about their rules for choosing goals or their reasons for choosing possible actions, since if they did they, would regress to the competent level. Rather, they reflect upon the goal or perspective that seems evident to them and upon the action that seems appropriate to achieving that goal.. Let us call the kind of inferential reasoning exhibited by the novice, advanced beginner and competent performer as they apply and improve their theories and rules, "calculative rationality", and what experts exhibit when they have time, "deliberative rationality." Deliberative rationality is detached, reasoned observation of one's intuitive, practice-based behavior with an eye to challenging, and perhaps improving, intuition without replacing it by the purely theory-based action of the novice, advanced beginner or competent performer.. For example, sometimes, due to a sequence of events, one is led to see a situation from an inappropriate perspective. Seeing an event in one way rather than some other almost-as-reasonable way, can lead to seeing a subsequent event in a way quite different from how that event would have been interpreted had the second perspective been chosen. After several such events one can have a totally different view of the situation than one would have had if, at the start, a different reasonable perspective had been chosen. Getting locked into a particular perspective when another one is equally or more reasonable is called "tunnel vision." An expert will try to protect against this by trying to see the situation in alternative ways, sometimes through reflection and sometimes by consulting others and trying to be sympathetic to their perhaps differing views. The phenomena suggest that the expert uses intuition not calculation even in reflection.

If this were merely an academic discussion, we could conclude here, simply correcting the traditional account of expertise by replacing calculative with deliberative rationality; if it were merely a matter of business, we could sell out stock in expert systems companies. Indeed, it turns out that would have been a good idea, since they have almost all gone out of business. But we cannot be so casual. The Socratic picture of reason underlies a general movement towards calculative rationality in our culture, and that movement brings with it great dangers.

The increasingly bureaucratic nature of society is heightening the danger that in the future skill and expertise will be lost through over reliance on calculative rationality. Today, as always, individual decision-makers understand and respond to their situation intuitively as described in the highest levels of my skill acquisition model. But when more than one person is involved in a decision, the success of science and the availability of computers tend to favor the detached mode of problem description characteristic of calculative rationality. One wants a decision that affects the public to be explicit and logical, so that rational discussion can be directed toward the relevance and validity of isolated elements used in the analysis. But, as we have seen, with experience comes a decreasing concern with accurate assessment of isolated elements. In evaluating elements, experts have no expertise.

For example, judges and ordinary citizens serving on our juries are beginning to distrust anything but "scientific" evidence. A ballistics expert who testified only that he had seen thousands of bullets and the gun barrels that had fired them, and that there was absolutely no doubt in his mind that the bullet in question had come from the gun offered in evidence, would be ridiculed by the opposing attorney and disregarded by the jury. Instead, the expert has to talk about the individual marks on the bullet and the gun and connect them by rules and principles showing that only the gun in question could so mark the bullet. But in this he is no expert. If he is experienced in legal proceedings, he will know how to construct arguments that convince the jury, but he does not tell the court what he intuitively knows, for he will be evaluated by the jury on the basis of his "scientific" rationality, not in terms of his past record and good judgment. As a result some wise but honest experts are ignored, while non-expert authorities who are experienced at producing convincing legal testimony are much sought after. The same thing happens in psychiatric hearings, medical proceedings, and other situations where technical experts testify. Form becomes more important than content. It is ironic that judges hearing a case will expect expert witnesses to rationalize their testimony, for when rendering a decision involving conflicting conceptions of what is the central issue in a case and therefore what is the appropriate guiding precedent, judges will rarely if ever attempt to explain their choice of precedents. They presumably realize that they know more than they can explain and that ultimately unrationalized intuition must guide their decision-making, yet lawyers and juries seldom accord witnesses the same prerogative.

In each of these areas and many more, calculative rationality, which is sought for good reasons, means a loss of expertise. But in facing the complex issues before us we need all the wisdom we can find. Therefore, society must clearly distinguish its members who have intuitive expertise from those who have only calculative rationality. It must encourage its children to cultivate their intuitive capacities in order that they may achieve expertise, not encourage them to reason calculatively and thereby become human logic machines. In general, to preserve expertise we must foster intuition all levels of decision making, otherwise wisdom will become an endangered species of knowledge.]