More details come out about the Tucson shooter Jared Loughner’s insanity.  I was struck with this paragraph in a description of his delusions (none of which were apparently related to politics, despite what is still being said):

Slowly but steadily, his intelligence warped into a distorted, disconnected series of obsessions. He developed an illogical fascination with logic. Math, grammar, logic – the systems civilization has developed to make sense of the world became the means through which he expressed the confusion and pain in his increasingly lost mind.

via Friends, teachers tell of Loughner’s descent into world of fantasy.

This reminds me of G. K. Chesterton’s comment in Orthodoxy that a madman is not someone who has lost his reason, but someone who has lost everything but his reason.  Chesterton pointed out that madmen often carry a kind of logic to its extreme–circular reasoning, seeing evidence of conspiracies everywhere, closely analyzing ordinary occurrences and finding sinister meanings–but they lack normal human feelings and perspectives.