 What about premise  (2)?  Again, a serious case can be made for its truth. Such a case first compares source physicalism, not to omni-theism, but to its opposite, source idealism. Source idealists believe that the mental world existed before the physical world and caused the physical world to come into existence. This view is consistent with both ontological idealism and ontological dualism, and also with physical entities having both physical and mental effects. It entails, however, that all physical entities are, ultimately, causally dependent on one or more mental entities, and so is not consistent with ontological physicalism. The symmetry of source physicalism and source idealism is a good pro tanto reason to believe they are equally probable intrinsically. They are equally specific, they have the same ontological commitments, neither can be formulated more elegantly than the other, and each appears to be equally coherent and equally intelligible. They differ on the issue of what is causally dependent on what, but if Hume is right and causal dependence relations can only be discovered by observation and not a priori, then that won’t affect the intrinsic probabilities of the two hypotheses.