Science, for James Croll, began and ended in metaphysics. Metaphysics, in turn, provided proof of a First and Final Cause of all things. This proof rested on two metaphysical principles: that every event must have a cause, and that the determination of a cause is distinct from its production. This argument emerged from his deeply held religious commitments. As a 17-year-old, he converted to a Calvinist and evangelical form of Christianity. After a period of questioning the Calvinist system, he embraced it again through reading the famous treatise on the will by the New England theologian, Jonathan Edwards. This determinedly metaphysical work, which engaged as much with Enlightenment thought as with Calvinism, defended the view that the will was not a self-determining cause of human action. This ‘hard case’ provided the basis for a larger claim that every act whatever has a cause, and that the production of an act was different from its determination. In part through reading Edwards, Croll remained a devout and convinced ‘moderate’ Calvinist for the rest of his life. He also developed a deep love of metaphysics and became convinced that without it, everything, including science, remained confused and in darkness. For Croll, even the most basic science could not be properly conducted without prior metaphysical principles. But this was more than just an argument about the philosophical foundations of scientific inquiry. It was also based on Croll's conviction that the cosmos, earth history and life (including his own) was fully determined by a supreme and perfect intellect. This conviction entered into the marrow of Croll's scientific theories and shaped his interpretation of the twists and turns of his own life. In short, to take seriously Croll's own self-understanding, we need to allow him to ‘do God’.