Lewis’s Argument for Identity Theory

1. Experiences are partly defined by the behavioral manifestations they cause.
2. So, experiences are causes of physical phenomena. (by 1)
3. Correct physics completely accounts for all physical phenomena in terms of other physical phenomena.
4. Behavioral manifestations are physical phenomena.
5. So, all the causes of behavioral manifestations are physical phenomena. (by 3 and 4)
6. So, experiences are physical phenomena. (by 2 and 5)

An Argument Against Explanatory Closure of Physics

1. If only physical phenomena explain physical phenomena, then some physical phenomena are unexplained.
2. So, (a) some physical phenomena are explained by non-physical phenomena or (b) some physical phenomena are unexplained (or both).
3. It is more likely that some physical phenomena are explained by non-physical phenomena than that some physical phenomena are unexplained.
4. So, the probability that some physical phenomena are explained by non-physical phenomena is greater than 1/2.