The traditional account of skills
The rationalist philosophical tradition which descends from Socrates, to Plato, to Leibniz, to Kant, to conventional AI and knowledge engineering takes it for granted that understanding a domain consists in having a theory about that domain. A theory formulates the relationships between objective, context-free features (attributes, factors, data points, cues, etc.) in terms of abstract principles (covering laws, rules, programs, etc.) As this tradition develops, even everyday practice is assumed to be based on unconscious theory.
In one of his earliest dialogues, The Euthyphro, Plato tells us of an encounter between Socrates and Euthyphro, a religious prophet and so an expert on pious behavior. Socrates asks Euthyphro to tell him how to recognize piety: “I want to know what is characteristic of piety … to use as a standard whereby to judge your actions and those of other men.” But instead of revealing his piety-recognizing principles, Euthyphro does just what every expert does when cornered by Socrates. He gives him examples from his field of expertise; in this case situations in the past in which men and gods have done things which everyone considers pious. Socrates persists throughout the dialogue in demanding that Euthyphro tell him his rules, but although Euthyphro claims he knows how to tell pious acts from impious ones, he cannot state the rules which generate his judgments. Socrates ran into the same problem with craftsmen, poets, and even statesmen. None could articulate the theory underlying his behavior.