Reasons and reasoning were central to the work of Paul Grice, one of themost influential and admired philosophers of the late twentieth century. Inthe John Locke Lectures that Grice delivered in Oxford at the end of the1970s, he set out his fundamental thoughts about these topics; Aspects ofReason is the long-awaited publication of those lectures.The focal point is an investigation of practical necessity (the necessity of'I must not torture' or 'I must go to law school' for example). Gricecontends that practical necessities are established by derivation; they arenecessary because they are derivable. Aspects of Reason sets this claim inthe context of an account of reasons and reasoning. This allows Grice todefend his treatment of necessity against obvious objections, also revealinghow the construction of explicit derivations can play a central role inexplaining as well as justifying thought and action. Grice was still workingon Aspects of Reason during the last years of his life; unpolished as it is,the book provides an intimate glimpse into the workings of his mind. Thisrich and subtle work, powerfully evocative of its author, will refresh andilluminate many areas of contemporary philosophy.