Which is right? “Can not” or “cannot”?

Habit tells me “cannot,” but I can’t find this peculiar spelling in the index of any of my style guides.

However, Wikipedia gives me this quote, in which I’ve added the bolding to “cannot”:
In this regard, the following quotation from The Chicago Manual of Style deserves notice:

Rules and regulations such as these, in the nature of the case, cannotbe endowed with the fixity of rock-ribbed law. They are meant for theaverage case, and must be applied with a certain degree of elasticity.

I haven’t thought about this issue in years. I usually work around it by using “can’t.”

What’s your practice?

This is a reposting of one of the most popular posts on one of my predecessor blogs. I originally posted it in April 2006.