What is insanity? What is sanity? For a concept as central to our mental well-being as this, it seems maddeningly vacuously defined.

My knowledge of psychology and the things I've read both point towards an answer that can be summed up thus: A mental illness is any mental problem that significantly harms normal activity.

Possibly excepting clear cases of missing brain bits or faulty wiring, insanity is defined by deviance from society's dominant reality paradigm. A person considered tidy and neat under one could be diagnosed with OCD in another. It's telling that in various places, at various times, disagreeing with the accepted world-view meant refusing to accept the true way of things and was grounds for mental illness.

Make no mistake - our various societies all have a number of idiosyncrasies and faults, from the massive to the smaller, prompting the insightful, the observant and the arrogant to famously wonder: "Am I insane, or is everyone else insane?" Not a one is non-mad. Not all the way through. And when madness is found, by definition the one sane thing to do is to excise it.

Insanity always is the sane response to a mad society.

"A time is coming when men will go mad, and when they see someone who is not mad, they will attack him saying, "You are mad, you are not like us."
-St. Anthony of Egypt