"Who in the rainbow can draw the
where the violet tint ends and the orange tint begins?
Distinctly we see the difference of the colors,
but where exactly does the one firest blending enter into the other?
So with sanity and insanity.
In pronounced cases there is no question about them.
But in less obvious cases,
few people are willing to draw the exact line of demarcation
...though for a fee some professional experts will."
---Herman Melvill, Billy Budd