http://newhumanist.i2p/articles/466/materialism-mechanism-and-the-human-mind
Materialism, according to the mathematician Norman Levitt, "refers to the view that there is essentially only one kind of reality, one kind of material existence, governed by its unique and invariable set of laws". There is, however, more than one way to understand 'materialism'. One definition is that the only stuff that exists is physical matter.