Aquinas clearly believes that human beings have Free Choice. In De Malo, he argues that without choice, there would be no grounds for praise or blame, reward or punishment, or moral philosophy. He claims that the human will is necessarily moved toward what it perceives as good, but choice comes in with the variation that arises for the following reasons:
1) Reason moves us to prefer one good over another (perhaps by some weighing process).
2) We notice or fail to notice some aspect of the good rather than another.
3) Our dispositions cause us to tend toward one kind of good rather than another.
David Hume points out that if human decisions are merely the product of reasons, temperaments, and dispositions, then there is really no reason to think that a person would do anything other than what they did in a given situation. Their behavior is completely explained on the basis of these things, none of which really involve choice.
3) does not involve free choice because dispositions are caused by previous experiences and choices. That is, 3) does not highlight a real opportunity for the agent to affect the system as 3) is merely the product of previous experiences. Just because a computer has the ability to alter its own code or have its code altered by some outside force does not mean that the computer could have done something different than what it did in a given scenario.
2) does not involve free choice because one’s noticing is not wholly voluntary. Either one happens to notice a thing or does not. And one might decide to continue looking for goods in a given situation. But the decision to examine the situation more carefully before proceeding is a sub-conclusion to the decision making process. Consider the optical character recognition that comes standard on most computer scanners. Just because the scanner fails to recognize a character does not mean that it chose to do so. And, even if the scanner’s software has a way of deciding to re-scan the object, this does not mean that it could have done otherwise.
1) is more difficult because Aquinas does not say how a person decides to prefer one good over another. Hume continually calls attention to the fact that people concern themselves with the spatially and temporally near rather than distant goods. One might weigh options in a utilitarian fashion. So long as there is a psychological model of a criterion by which a person makes decisions, the choice seems determined. And even if the agent gets to choose the criterion, one must ask by what criterion he chose that criterion.Thus, Hume seems to demonstrate that Aquinas’s model fails to include an unnecessary element. There is no praiseworthy or blameworthy element in the account. And Aquinas’s model of choice falls prey to the very criticism he was hoping to avoid.