Book excerpt: Towards Non-Being presents an account of the semantics of intentional language - verbs such as 'believes', 'fears', 'seeks', 'imagines'. Graham Priest's account tackles problems concerning intentional states which are often brushed under the carpet in discussions of intentionality, such as their failure to be closed under deducibility. Drawing on the work of the late Richard Routley (Sylvan), it proceeds in terms of objects that may be either existent or non-existent, atworlds that may be either possible or impossible. Since Russell, non-existent objects have had a bad press in Western philosophy; Priest mounts a full-scale defence. In the process, he offers an account of both fictional and mathematical objects as non-existent.The book will be of central interest to anyone who is concerned with intentionality in the philosophy of mind or philosophy of language, the metaphysics of existence and identity, the philosophy or fiction, the philosophy of mathematics, or cognitive representation in AI.