I think causal determinism is more plausible than free will. Causal Determinism is the thesis that the course of the future is entirely determined by the conjunction of the past and the laws of nature. Consider a proposition “P” that describes the way that the entire universe was at some point in the past. Also imagine a proposition that expresses the conjunction of all the laws of nature; call this proposition “L.” Determinism then is the thesis that the conjunction of P and L entails a unique future. Given P and L, there is only one possible future, one possible way for things to end up. The claim for determinism falls under empiricism, as the truth of determinism is contingent. That is, determinism is neither necessarily true nor necessarily false. Therefore, I think it is to be discovered by investigating the way the world is, not through philosophical argumentation. I think determinism is plausible because the truth of determinism would entail that the laws of nature are not merely probabilistic, for if they were, then the conjunction of the past and the laws would not entail a unique future. Our observation of natural reality points towards a deterministic world. For instance, Many physical phenomena such as the motion of planets, chemical reactions, and biological processes are predictable and operate according to deterministic principles. One might argue that quantum mechanics poses a challenge towards determinism, as in the quantum realm phenomena are probabilistic rather than deterministic. However, that is only true given the copenhagen interpretation of QM. There are also deterministic interpretations of QM, such as the many-worlds interpretation. Even if QM points towards an indeterministic world, it would have little implications on our discussion. Even if systems of micro-particles such as quarks are indeterministic, it might be that systems involving larger physical objects such as cars, dogs etc are deterministic. It is possible that the only indeterminism is on the scale of micro-particles and that macro-objects themselves obey deterministic laws. Moreover, I think probabilistic laws don't necessarily negate determinacy and only reflect our epistemic limitations. For instance, we often use probabilities in weather forecasting not because weather is indeterministic, but because we cannot account for all variables with precision.
