 In the theoretical part (physica generalis) of his Physica Electiva, Sturm sets down the metaphysical foundations of his system. In a nutshell, Sturm argues that the whole of nature (human and angelic minds set aside) can be explained by two principles: matter and its modes, which are material forms. Both these principles are causally passive and shaped by local motion. Forms, in particular, provide the specific reasons why certain phenomena are produced in a certain way, but they do not include the causal powers that bring these phenomena about. That power comes only from God, who is the universal and omnipresent cause acting in nature. In order to support this picture, Sturm gives a number of original twists to an argumentative strategy already exploited by other occasionalist authors, while providing at the same time a more eclectic and broader rationale for endorsing an occasionalist metaphysics. To deepen Sturm’s account, three main points deserve special attention: (1) the justification for passive forms as modes of matter; (2) why God’s causal power is directly needed to bring about natural phenomena; and (3) the role that passive forms play in scientific explanations.