Source: (2005) Columbia Law Review. 105: 1162-1189.Why do sentencing systems require guidelines? This is basically the question R.A. Duff asks at the beginning of this paper. Building on that question, Duff addresses the form that such guidelines should take. In particular, Duff looks at objections to numerical guidelines schemes. This leads to an appeal to an alternative, Aristotelian conception of practical reasoning to argue that a just and rational sentencing system should be based on a discursive rather than numerical set of guidelines. On this basis, Duff discusses how non-custodial sentences – which are central to a humane penal system – can be brought under a guidelines scheme. One way to do this would be to adopt a negotiated sentencing in which the offender participated in the determination of the sentence. This would shift attention to a greater emphasis on the justice of sentencing procedures rather than justice conceived in terms of the sentence apart from the procedures.