Dictionary.com defines this phrase as meaning “a plan behind a person’s apparently inexplicable behavior.” The source is no mystery. Phrase Finder notes this phrase came from Shakespeare’s Hamlet, 1602, but it has been adapted over time. The actual line from the play is ‘Though this be madness yet there is method in it‘.

Interestingly, the Oxford Dictionaries lists the quote in the modern form: “whatever he was about, there was method in his madness [From Shakespeare’s Hamlet ( ii. ii. 211)]”

Sparknotes clears this up by presenting the original text and modern adaptation side by side:

• Original – POLONIUS says (aside) Though this be madness, yet there is method in ’t.—(to HAMLET) Will you walk out of the air, my lord?
• Modern – POLONIUS says (to himself) There’s a method to his madness. (to HAMLET) Will you step outside, my lord?

I’m happy to see the modern version, though the translator isn’t cited. I’ve never been very fond of Shakespeare because it’s practically a foreign language. I’m sure some people will, however, be horrified at the translation.

It sometimes seems as if Shakespeare coined half of the English language.