1. A knowledge system comprising a computer having a memory, said memory storing a knowledge base encoding knowledge about a particular subject domain, said computer having a knowledge base interpreter for interpreting said knowledge base to solve specified problems pertaining to said subject domain and to indicate the methods of solution to a subject system, said memory further storing information about the status of the solution of said problems by said knowledge base interpreter, said knowledge base interpreter including means for changing said information about the status of the solution of said problems during said interpreting of said knowledge base, and an evaluation system communicating with said subject system and accessing the knowledge in said knowledge base, said evaluation system including means for probing said subject system about selected portions of said knowledge about said subject domain to obtain responses from said subject system, and means for comparing said responses from said subject system to said selected portions of said knowledge about said subject domain to evaluate the subject system's knowledge and performance with respect to said subject domain, said means for probing and said means for comparing being operative during the operation of said knowledge base interpreter, wherein said knowledge base further encodes knowledge defining a set of interrupt conditions of said status of said solution of said problems, and wherein said computer further includes means for determining whether any of said interrupt conditions occur in said status of the solution of said problems and thereupon interrupting the interpreting of said knowledge base to solve said problems and activating said evaluating system to probe said subject system about the interrupt condition having occurred so that the subject system's knowledge and performance are evaluated while the methods of solution to said specified problems are indicated to said subject system.