John Andrew Leslie is a Canadian philosopher who focuses on explaining the world’s existence. Educated at Wadham College, Oxford, he earned a BA in Psychology and Philosophy, then an MLitt in Philosophy. He is University Professor Emeritus at the University of Guelph, and a Fellow of the Royal Society of Canada. 

Leslie is the author of Universes (a philosophical study of multiple universes); of The End of the World: The Science and Ethics of Human Extinction; of Infinite Minds: A Philosophical Cosmology; and of Immortality Defended. He is the editor of Modern Philosophy and Cosmology, and co-editor with Robert Lawrence Kuhn of The Mystery of Existence: Why Is There Anything At All?, the first major edited volume (some fifty authors reprinted, going back to Plato and ending with philosophers, theologians and scientists of today) to tackle all the main ways of answering its question.

Leslie taught in the Department of Philosophy at the University of Guelph, Ontario, and chaired the Guelph-McMaster Doctoral Program in Philosophy. He had visiting positions at the Research School of Philosophy at Australian National University and the Institute of Astrophysics at the University of Liège, Belgium; and in 1998 toured Britain as the British Academy—Royal Society of Canada Exchange Lecturer.

Leslie’s chief fields of research are Metaphysics, with an emphasis on the nature of causation, of time, of the mind, and of the world’s unity; Philosophy of Religion, emphasizing Plato’s suggestion that an ethical need for the cosmos to exist is, all by itself, creatively powerful, and the Spinozistic notion that our universe is just the thoughts of a divine mind; Philosophy of Cosmology, particularly the idea that there exist many universes, ours being one of the rare ones in which intelligent living beings can evolve; Ethics, particularly the need to save humankind from annihilation by something such as warfare or pollution; and Probability Theory, particularly as applied to how long humankind is likely to survive.

In addition, Leslie invented Hostage Chess, a cross between western chess and Shogi.