Definitions of sanity:

One of the definitions of sanity, itself, is the ability to tell real from unreal. Shall we need a new definition? (ALVIN TOFFLER, Future Shock)... Sanity: the ability to recognize differences, similarities and identities. The legal definition of sanity is the "ability to tell right from wrong." The better one can tell differences, the more rational he is. The less one can tell differences, no matter how minute, and know the WIDTH of those differences and the closer one comes to thinking in identities (A=A=A=A...), the less sane he is. ... This is workable definition to check your own sanity about everything!