3.1 Tacit knowledge as a theoretical concept

In research by Sternberg and his colleagues (Sternberg et al., 1993; Sternberg et al., 1995; Wagner and Sternberg, 1985), the term tacit knowledge has been used to characterize a type of knowledge, the possession of which distinguishes more from less practically-successful individuals. In order to understand better the theoretical concept of tacit knowledge, we begin with a distinction between nominal and natural concepts.

Nominal concepts are used attributively. For example, we use the term "bachelor" to attribute certain features (i.e., male, adult, unmarried) to some objects or persons. The instances of a nominal concept often share features that are both necessary (i.e., all valid instances must have these features) and sufficient (i.e., having these features is enough to qualify something as a valid instance). Membership in a nominal concept is "all or none"—either an instance possesses the critical features or it does not.

Natural concepts, in contrast, are used ostensively. For example, we use the term "furniture" to refer to objects that we view as equivalent (e.g., dresser, chair, table). The instances of a natural concept share characteristics features, but these features are not necessary or sufficient for membership. Membership in a natural concept is not "all or none," but rather instances are judged in terms of their strengths of resemblance to the concept. This means that some instances (those with high resemblance) will be judged as better examples of the concept than will other instances (those with low resemblance). For example, most people would agree that "arm chair" is a more typical example of the concept "furniture" than is "bean bag chair."

Tacit knowledge is a natural concept. It is used to denote a type of knowledge that is held together by the resemblance of items to one another and not by a set of individually-necessary and jointly-sufficient features. This lack of necessary and sufficient features does not mean that as a concept tacit knowledge is incoherent or meaningless. Two people may not be able to identify the critical features that all items of furniture share, but they can still agree that furniture exists and that a coffee table is furniture and a toaster oven is not.

Because tacit knowledge is a natural concept, we do not expect that judgments about what is and is not tacit knowledge will be "all or none." Rather judgments should depend on the item's strength of resemblance to the concept. Some knowledge will seem to represent a particularly clear example of tacit knowledge and other knowledge will seem marginal. For marginal items, individuals may disagree about whether the item is a valid instance of tacit knowledge. Given a high level of agreement among judges, the tacit quality of knowledge items can be determined with some degree of confidence.

We describe below three key features that are commonly shared by items of tacit knowledge. These features are used to judge the resemblance of items to the concept. In other words, items that possess these features are more likely to be characteristic of tacit knowledge.

3.2 The characteristic features of tacit knowledge

We identify three key features of tacit knowledge. These features of tacit knowledge relate to (a) the conditions under which it is acquired, (b) its cognitive structure, and (c) the conditions of its use. First, tacit knowledge generally is acquired on one's own with little support from the environment (e.g., through personal experience rather than through instruction). Second, tacit knowledge is viewed as procedural in nature. It is associated with particular uses in particular situations or classes of situations. Third, because it generally is acquired through one's own experiences, tacit knowledge has practical value to the individual. We expand upon each of these features below.