A theory of madness

Is there a difference between a person who is sane and that person when he is, in some way, mad? By extension, do the states of affairs we speak of as psychoses, neuroses, personality disorders, and adjustment reactions display any common features? We need adequate and coherent answers to these foundational questions if the persons about whom these judgments are made are to be properly perceived and if psychiatry as a historically emergent institution is to be rendered moderately intelligible.