This chapter develops the distinction, introduced in Chapter 4, between offences and justificatory defences. Following Kenneth Campbell, it explains the distinction as corresponding to a distinction between reasons against and reasons in favour of an action (‘pros and cons’). But the correspondence is complex. It details some of the complexities, showing how conflicts of reasons are sometimes structured by second-order reasons, and showing how this affects the contrast between offences and justificatory defences. The chapter explains how justificatory arguments are nested in excusatory ones, such that the concept of a justification has logical priority over that of an excuse. The chapter also assesses the significance of some of this for the criminal law, in particular for the ideal of the rule of law. It explains how, consistently with the rule of law, the scope of defences (unlike the scope of offences) can freely be left to judges to determine ex post facto.
Keywords: criminal law, defences, excuse, second-order reasons, rule of law,