In our culture, people deemed "mad" are often defined as different or other. But what is "madness"?

Common sense is quick to label people mentally ill the minute they fail to behave normally, stop thinking or living like ourselves. But what is "madness," really? Melancholy, the malaise caused by life's trials and tribulations, or even excessive, sometimes delinquent, and criminal behavior—how can we differentiate between these and madness itself, which falls within the purview of psychiatry? Madness is unique to human beings, for after all, they are the only ones capable of committing suicide from despair or murdering their fellows. Yet the descent into madness remains an enigma...