 In philosophy, the classical theory has been subjected to a number of criticisms but perhaps the most fundamental is that attempts to specify definitions for concepts have a poor track record. Quite simply, there are too few examples of successful definitional analyses, and certainly none that are uncontroversial (Wittgenstein 1953/1958, Fodor 1981). The huge literature on the analysis of knowledge is representative of the state of things. Since Edmund Gettier (1963) first challenged the traditional definition of KNOWLEDGE (as JUSTIFIED TRUE BELIEF), there has been widespread agreement among philosophers that the traditional definition is incorrect or at least incomplete (see the entry  the analysis of knowledge)).  But no one can seem to agree on what the correct definition is. Despite the enormous amount of effort that has gone into the matter, and the dozens of papers written on the issue, we are still lacking a satisfactory and complete definition. It could be that the problem is that definitions are hard to come by. But another possibility—one that many philosophers are now taking seriously—is that our concepts lack definitional structure.