Dreams are not merely the succession of visual images, but rather experiences of living in a world of events, actions, and emotions. The widespread belief in the significance of dreams, either as prophecies or divine messages, or as especially valuable indicators of psychological truths, as in the work of Freud and Jung, has little empirical support. Although actual dreams have a nature and a content that is parasitic upon normal experience, since the things in our dreams are persons and objects of a kind with which we are generally familiar, philosophically dreams have been a convenient image of the possibility of total dissociation between what a subject experiences, and how things are in the real world. Hence they form a central metaphor in epistemology; one of the first questions in philosophy is sometimes posed as ‘How do I know I am not now or always dreaming?’ (See method of doubt.) Dreams also provide a test case for philosophers trying to deny the reality of private experience knowable only to the subject.