This book develops a new approach to the mind called mental fictionalism. The key idea behind this approach is that the mind is a useful fiction. The book begins with our ordinary conception of the mind (known as folk psychology). At present, the dominant interpretation of folk psychology sees it as an attempt to describe our inner machinery (a view the author calls Cartesianism). The representational theory of mind (or representationalism) argues that our folk theory is true, and that our thoughts (especially our propositional attitudes, such as beliefs and desires) are representations inside our heads. Mental fictionalism offers a new interpretation of folk psychology. According to mental fictionalism, when we attribute beliefs and desires, we do not claim that people have representations inside their heads; we merely pretend that they do. Our ordinary conception of the mind is fundamentally metaphorical: we project the ‘outer world’ of human culture (especially language) onto the ‘inner world’ of the mind. This is an enormously useful way of making sense of people and their behaviour. But we should not forget that this inner world is only a fiction.