The analysis of the concept of knowledge is understandably regarded as central to the development of an adequate philosophical system. And yet, as is also apparent, no proposal of recent date has succeeded in meeting certain well-known objections, counterinstances, anomalies. It is reasonable, therefore, to step back from these would-be direct contributions to review the principal strategies by which the relevant puzzles may be supposed to be managed.

Undoubtedly, it was Roderick Chisholm's recovery and revision of the account of the Theaetetus that encouraged a sustained effort, by various hands, to formulate a definition of knowledge in terms of its necessary and sufficient conditions.