Intellectual property law is not prepared for a world where non-humans create significant inventions, music, literature, and art. Generative artificial intelligence's ability to produce valuable properties without attributable authorship defies the theories of ownership that underlie modern intellectual property law. These authorless properties can be readily assigned ownership, however, under the more ancient rules of real and personal property. Lawmakers should rely on these common law rules in developing a new branch of intellectual property law that accommodates exclusive human ownership of AI-generated properties.This Article demonstrates how, under the contemporary American intellectual property regime, the ownership of AI-generated properties is troublingly uncertain. Because neither the artificial intelligence nor the person who entered the prompt can readily claim authorship, these properties could arguably be owned by the state, the developer of the artificial intelligence, the authors of the material on which the artificial intelligence was trained, or nobody at all. This Article shows how principles like the law of capture and the doctrine of accession can easily resolve this problem of authorship, vesting ownership in the place where it makes the most sense, promoting efficiency, fairness, and innovation. The Article addresses and rebuts the arguments against applying the rules of personal property to intellectual property. It concludes that the certain past, rather than the speculative future, offers the best foundation for assigning ownership over this new and important branch of property law.