J.S. Mill famously equated physical things with "permanent possibilities of sensation." This view, known as phenomenalism, holds that a rock is a tendency for experiences to occur as they do when people perceive a rock, and similarly for all other physical things. In Phenomenalism, Michael Pelczar develops Mill's theory in detail, defends it against the objections responsible for its current unpopularity, and uses it to shed light on important questions in metaphysics, the philosophy of science, and the philosophy of mind. Identifying physical things with possibilities of sensation establishes a transparent connection between the world of physics and the world of sense, provides an attractive alternative to currently fashionable structuralist and panpsychist metaphysics, offers a fresh perspective on the problem of consciousness, and yields a satisfying theory of perception, all by taking two things notoriously resistant to reduction, chance and experience, and constructing everything else out of them.