In his philosophy of psychology, Wittgenstein explicates those epistemological objectives, which are manifested in the phenomena of madness, trying to find some answers to them. Therewith, he questions some psychiatric categories, which seem to obstruct a more productive understanding of insanity. In this paper, Fischer tries to reconstruct Wittgenstein's argumentation lines, and to form some propositions towards a theory of mental illness. These propositions are supposed to overcome Jasper's dictum of incomprehensibility, which - meant to be a psycho pathological term - says that the creations of madness are on principle impossible to understand. Thus, insanity can be conceived as an altered cognition based on a change of grammar. Serving as a foundation of deviant language games, this grammar is - in a recursive way - related to the experiencible and experienced reality. Wittgenstein's constructivist understanding of semantics may serve as an instrument which allows for a more comprehensive access to "lunatic language games", and thus bridging the presumed gap in the understanding of insanity.