Although the expression “tacit knowledge” appears to have been introduced by Michael Polanyi (1958/1974), the idea that certain cognitive processes and/or behaviors are undergirded by operations inaccessible to consciousness — by a cognitive unconscious, as Reber (1995) calls it — goes back at least as far as Helmholtz’s work in the 19th century (Reber 1995, p. 15). A more recent and influential formulation of this basic idea can be found in Lashley (1956).
Varieties of Tacit Knowledge
The distinction between tacit knowledge and explicit knowledge has sometimes been expressed in terms of knowing-how and knowing-that, respectively (Ryle 1949/1984, pp. 25-61), or in terms of a corresponding distinction between embodied knowledge and theoretical knowledge. On this account knowing-how or embodied knowledge is characteristic of the expert, who acts, makes judgments, and so forth without explicitly reflecting on the principles or rules involved. The expert works without having a theory of his or her work; he or she just performs skillfully without deliberation or focused attention. Knowing-that, by contrast, involves consciously accessible knowledge that can be articulated and is characteristic of the person learning a skill through explicit instruction, recitation of rules, attention to his or her movements, etc. While such declarative knowledge may be needed for the acquisition of skills, the argument goes, it no longer becomes necessary for the practice of those skills once the novice becomes an expert in exercising them, and indeed it does seem to be the case that, as Polanyi argued, when we acquire a skill, we acquire a corresponding understanding that defies articulation (Polanyi 1958/1974).
But the distinction between knowing-how and knowing-that breaks down upon examination. As Dretske has pointed out (Dretske 1988, p. 116), knowing-how involves more than just a certain technical or physical “know-how”; it also involves knowing how to obtain desired end-states, knowing what to do in order to obtain them, and knowing when to do it.