Capacity may be considered as an underlying ability or in its particular relation to one act. A person having the general possibility of choosing good or evil does not mean that two contradictory acts are both occurring at once.
Choosing disbelief rather than belief concerns the direction of the capacity’s relation. It does not automatically show the loss of every prior capacity for the alternative. This is why a difference in the essence of power must be distinguished from a difference in the act toward which it is directed.
To clarify the debate, first ask whether the claim concerns general eligibility or the specific occurrence of an act.