The patent system appears to make three metaphysical assumptions often associated with scientific realism: there is a natural (i.e. external) world that is independent of human knowledge and technology; unobservable entities (such as some types of inventions) exist; and objects can have causal powers. Although a straightforward reading of patent laws implies these metaphysical commitments, it is not at all clear that what the patent system has to say about the world has any bearing on issues of scientific realism. While realists might embrace the patent system's apparent metaphysics as providing additional support for their view, anti-realists could propose an alternative interpretation of patent law that does not involve realist metaphysical commitments. Thus, questions about the patent system's metaphysics depend on whether one takes patent law at face value or defends an interpretation of patent law motivated by philosophical theory. Nevertheless, philosophers of science should pay attention to the practice of patenting, even if they ultimately reject the patent system's apparent metaphysics and offer an alternative interpretation.