A quick Thomistic argument for alternate possibilities

1. I freely choose between A and B only if I am deciding in the light of a non-dominated reason for A and a non-dominated reason for B.
2. A non-dominated reason for C is a causal power for deciding in favor of C.
3. If x has a causal power for φing, then x can φ.
4. So, if I freely choose between A and B, then I can decide in favor of A and I can decide in favor of B.