A formalization of the argument from mental causation
1. Physical states are indeterminate with respect to intentional content. Given the state of the physical, there is a plurality of intentional states that are logically compatible with the state of the physical. In fact, any set of physical facts is logically compatible with the complete nonexistence of intentional states whatsoever.
2. If a broadly materialist world-view is correct, then the physical is causally closed. Nothing over and above the physical state of the world can be responsible for a subsequent physical or mental state.
3. Therefore, if there are mental states, and those mental states have determinate mental content, then that determinate mental content is causally irrelevant to the future course of nature.