Publications of recent years testify to perennial interest to problem of philosophy and psychiatry. “An affinity” of considered dichotomy concerns absence of “real” tool of diagnostic in psychiatry and in cognition of universal regularities in philosophy. Both in philosophers and in psychiatrists there are no special devices of cognition of the individual. This is only an imprinted virtual knowledge in difference from other diseases, where problem of computer primacy in diagnostic occurred. Here example with cognition of consciousness in psychiatry and philosophy may be introduced; the latter gives comprehensive definitions of this concept. In psychiatric practice, there is no tool, which could recognize delirium or amentia. This is only clinical experience of the doctor - the only “tool” of cognition - originally reflecting social-biological duality of nature of the individual. Summarizing medical experience is a particular method of scientific cognition. Theory of diagnosis considers diagnostic process as gnoseological - philosophical - in its essence. Diagnosis represents by itself complex cognitive process, which essence, as well as every cognitive process, consists in reflection of objectively existing regularities in consciousness of the individual. Understanding of the general, as gnoseological criterion of cognition, may serve a proof that namely community acts as a basic criterion of sum of information about considered by us social phenomenon - mental disorder. It has been noticed that knowledge of general appears to be the most effective in development of scientific investigations and in obtaining of new results.