If you argue with a madman, it is extremely probable that you will get the worst of it; for in many ways his mind moves all the quicker for not being delayed by the things that go with good judgment.

He is not hampered by a sense of humour or by charity, or by the dumb certainties of experience.

He is the more logical for losing certain sane affections.
Indeed, the common phrase for insanity is in this respect a misleading one.

The madman is not the man who has lost his reason.

The madman is the man who has lost everything except his reason.
The madman's explanation of a thing is always complete, and often in a purely rational sense satisfactory.