Naturalistic explanations can work as descriptions of actual causal relations among reals only if nominalism is false, so that their terms – mass, extension, momentum, 2, h, valence, π, spin, c, equilibrium, homeostasis, system, organism, state, fitness, and so forth – truly refer. Otherwise, they are nothing but vain wind.
But the falsity of nominalism entails the reality of the Forms. It entails supernaturalism.
Iff is a biconditional; LaPlace if and only if Plato, *and vice versa.* Now how can we say that Plato is true if and only if LaPlace is true? Are not the Forms prior to any of their instantiations?
The natural world can only be something or other if it is through and through constituted of instantiations of some forms or others. But likewise, the forms can be forms in the first place only of some actual things or other. You can’t get inactual forms any more than you can get formless actuality.
Prior to all worlds, then – i.e., prior to any particular instances of any Forms – the Forms must be all somehow actual. Only thus can there be such a thing as a natural world, with its intelligible nature, and thus its naturalistic explanations.