We frequently talk about meaning, understanding, and believing as mental states, processes, or mechanisms. Wittgenstein argues that any such appeal to mental phenomena is simply an attempt to give an occult explanation of something we have trouble graspin g. In saying something is a mental mechanism, we free ourselves from the responsibility of giving a clear account of how that mechanism works, as we would have to do in order to explain physical mechanisms.

Wittgenstein shows us the faultiness of this conception in a number of ways, including using language games to show that there is no one distinct process that characterizes all cases of meaning, understanding, and believing. He also runs through a number of thought experiments that break down the distinction between inner and outer. If understanding a rule is simply a matter of having that rule appear before one's mind, then this understanding should be able to consist of having that rule appear before on e's eyes—say, written on a piece of paper. There is nothing about this mentalistic conception of how we understand rules that makes this mental process somehow distinct from, and more useful than, a physical process.