This paper argues that inertia is an inherent principle and that inertia and Newton’s First Law are in this way natural in the Aristotelian sense. Indeed, many difficulties concerning inertia and the First Law of Motion may be resolved by understanding them through an Aristotelian conception of nature. The paper proceeds by examining the characteristic activities of inertia, the Aristotelian idea of nature, various accounts of inertia as force and as inert, and the manner in which an Aristotelian conception of (...) nature improves on these accounts. It concludes that the unsuccessful attempts by physicists to find an extrinsic origin of inertia, though they may eventually lead to new discoveries, support the view that inertia is an inherent principle of nature. Newton himself understood the principle of inertia through an eclectic but largely nonAristotelian conception of nature and matter and by the problematic notion of a vis inertiae. However, Newton’s general philosophy of nature should be distinguished from the more specific content of the First Law and of inertia itself. A general Aristotelian conception of nature can resolve many of Newton’s difficulties. Thus, inertia and the First Law of Motion are reasonably regarded as natural in the general Aristotelian sense. (shrink)