The book introduces Ramsey's main doctrines and assesses their contemporary significance. In particular, Jérôme Dokic and Pascal Engel are interested in Ramsey's thoughts on truth and belief, and his pragmatic thesis that the truth of one's beliefs guarantees the success of one's actions. From this, it is a short step to what may be called "Ramsey's principle": the content of a belief is constituted by the success of one's actions. This principle finds its current expression in the work of philosophers who offer evolutionary conceptions of mental states, according to which the success conditions of a belief are constituted by its biological functions. (publisher, edited)