“The study of nature or of the spatiotemporal world. This was regarded as a task for philosophy before the emergence of modern science, especially physics and astronomy, and the term is now only used with reference to premodern times. Philosophical questions about nature still remain, e.g., whether materialism is true, but they would usually be placed in metaphysics or in a branch of it that may be called philosophy of nature.
“Natural philosophy is not to be confused with metaphysical naturalism, which is the metaphysical view (no part of science itself) that all there is is the spatiotemporal world and that the only way to study it is that of the empirical sciences. It is also not to be confused with natural theology, which also may be considered part of metaphysics.”
— Panayot Butchvarov in The Cambridge Dictionary of Philosophy, 2nd ed., 600.