Determinism should be the obvious starting point for both physicists and philosophers. The idea that any action or set of events can unfold outside of prior physical causes underlies the idea of free will, but it also essentially contradicts the law of causality: every event has an exact set of causes, prior conditions which map perfectly to the resulting effects of a given system. The claim that your actions are purely the result of your own decisions does not factor your thinking itself as being a fundamentally physical process, governed only by physics. Thinking is a natural process, founded on top of other natural processes, and bound ultimately by the greater forces of causality. Of course, quantum randomness on a fundamental level may alter the effects of these processes such that the future cannot be predicted, but it does not dispute the fundamentally physical, and thus causal, nature of thought.