Solipsism is the ultimate empirical theory of human existence. It is the metaphysical position that there is only one self-conscious person in the universe, i.e., the present selfconscious being reading these paragraphs. A weaker version is the position that one can know for certain that there is only one conscious person in the universe, oneself. The present study is the only book-length examination of solipsism. It treats the origin of solipsism in the works of St. Augustine and René Descartes as well as all serious attempts to refute the thesis of solipsism. Such attempts were made primarily by British empiricists, specifically by George Santayana. Santayana concludes that solipsism cannot be refuted. Watson also concludes that solipsism cannot be refuted. He examines attempts by Descartes, Berkeley, Hume, Kant, British Idealists, Logical Positivists, Sense Datum Philosophers, and in particular Nelson Goodman and Gilbert Ryle (they are just pathetic). The spector haunting Modern Philosophy is not the Ghost in the Machine; it is solipsism. Watson argues that the foundations of Western Philosophy are solipsistic, and that all the major figures recognize this and know that solipsism cannot be refuted, but nevertheless continue by ignoring it, by pretending that it cannot be taken seriously, by offering inadequate solutions, and by treating solipsism as a joke. Watson’s book is the only study of solipsism by a professional philosopher, other than Santayana, in which solipsism is taken seriously as a threat to Modern Philosophy