Second, knowledge acquired under low environmental support is more likely to have practical value. When knowledge must be acquired on one's own, the probability increases that some individuals will fail to acquire it. When some individuals fail to acquire knowledge, those who succeed may gain a comparative advantage. This advantage is expected to be lower when the knowledge is highly supported by the environment (i.e., explicity and effectively taught) because more people would be expected to acquire and use it. At the same time, knowledge acquired through one's own experiences should have more personal relevance to the types of situations one encounters in everyday life.

Finally, we associate knowledge acquired through experience with knowledge that is procedural in structure. Because procedural knowledge is more difficult to articulate and more poorly conveyed relative to declarative knowledge, its acquisition is more likely to be a function of experiential learning. By the same token, knowledge acquired through experience is more likely to be related to action because originally it was obtained in the context of performing a practical, everyday task.

Each of these features is viewed as a continuous, rather than discrete, dimension of tacit knowledge. That is, knowledge is not categorized as either possessing or not possessing these features, but rather it is a matter of degree. Some knowledge may be more well-supported by the environment than other knowledge. Similarly, some knowledge may have more practical value to the individual than other knowledge. Knowledge that is closer to one end of the continuum is considered more representative of tacit knowledge.

3.3 What tacit knowledge is not

We have identified above the features that help describe what type of knowledge we consider tacit knowledge to be. It is helpful also to distinguish tacit knowledge conceptually from other related concepts such as job knowledge, general cognition, and performance.

3.3.1 Tacit knowledge is not synonymous with job knowledge

Schmidt and Hunter (1993) suggested that tacit knowledge is merely a type of job knowledge. Tacit knowledge and job knowledge are viewed more appropriately as overlapping concepts. First, some, but not all, tacit knowledge pertains to job-related activities. Tacit knowledge can pertain to any personally-valued activity, including academic and social activities; it is more than job knowledge. Second, some, but not all, job knowledge is tacit. Job knowledge includes declarative and procedural knowledge, with some of the latter characterized as tacit. Job knowledge may be explicit and readily verbalized, as in the rules for operating a lathe or the steps used to compute simple interest, or the knowledge may be tacit, as in knowing what package design will likely sell a product.

Measures of tacit knowledge have the potential to explain individual differences in performance that are not explained by traditional measures of job knowledge, which tend to assess more declarative, explicit forms of knowledge (see e.g., Schmidt and Hunter, 1998). Individual differences in the skill or inclination to acquire and use tacit knowledge make it a potentially useful construct for understanding intelligent behavior in real-world settings, as well as for predicting success in such settings.

3.3.2 Tacit knowledge is not a proxy for general cognition

The skill or propensity to acquire tacit knowledge is viewed as a dimension of practical cognition that conventional skill tests do not adequately measure. Overall cognitive ability tests and similar tests, which are intended to measure so-called general cognition (g), are composed of problems that can be characterized as largely academic or abstract.