People familiar with Objectivism will remember an old article by Nathaniel Branden titled, “The Contradiction of Determinism,” (Objectivist Newsletter, May 1963). In it, he argues, not that the doctrine of free will is true, nor that determinism is false. Rather, he argues that if determinism is true, we cannot know it. And the reason we can’t know it is that, if determinism is true, no knowledge is possible at all.
The argument is that knowledge must be validated by a process of reason. Our suppositions about the world are not self-certifying. The mere presence of an idea in your mind does not establish that it is true. Therefore, we have to evaluate our suppositions about the world by means of sensory evidence and other tests, such as coherence. This must be done by a process of reason. But the process of reason cannot be realized by merely mechanical causation of the sort that is expressed by causal laws. Causal laws determine that a certain sort of event results in consequence of a certain sort of prior event, and this sort of determination is entirely different from that of seeing reasons or recognizing logical connections.