The Determination Fallacy is the mistaken idea that just because some of our decisions are determined by our motives and deliberations, it must mean that strict causal determinism or pre-determinism is true. Philippa Foot in 1957 correctly doubted that the ordinary language meaning of saying our actions are "determined" by motives has the same meaning as strict physical determinism, which assumes a causal law that determines every event in the future of the universe. Foot notes that our normal use of "determined" does not imply universal determinism.
For instance, an action said to be determined by the desires of the man who does it is not necessarily an action for which there is supposed to be a sufficient condition. In saying that it is determined by his desires we may mean merely that he is doing something that he wants to do, or that he is doing it for the sake of something else that he wants. There is nothing in this to suggest determinism. ("Free Will as Involving Determinism," The Philosophical Review, vol LXVI, (1957), p.441)The Determination Fallacy is somewhat related to the Science Advance Fallacy, the idea that because science, and especially neuroscience, is discovering more and more contributing causes of actions that we thought were the result of free decisions, that eventually all our decisions will be found to be the consequence of causes not in our control. It is also somewhat related to the Rational Fallacy, that free decisions must be rational decisions. For many philosophers, reason is the distinguishing characteristic of humanity. For theologians, reason is a gift of God along with the gift of free will. Another mistaken idea is that our decisions must be moral and our actions good in order to be free. This is another fallacy that we call the Ethical Fallacy.