However, cognitive science and psychology do not require the mind to be irreducible, and operate on the assumption that it has physical basis. In fact, it is common in science to presuppose a complex system; while fields such as chemistry, biology, or geology could be verbosely expressed in terms of quantum field theory, it is convenient to use levels of abstraction like molecules, cells, or the mantle. It is often difficult to decompose these levels without heavy analysis and computation. Sober has also advanced philosophical arguments against the notion of irreducibility.