This chapter discusses defences, which are a fundamental part of criminal law, and reflect important limitations on the proper scope of punishable conduct. It is the purpose of this chapter to set out and critique the law relating to defences, in both treaty-based and customary international law. This chapter is concerned with substantive defences; it does not deal with issues such as immunity, youth, ne bis in idem, or limitation periods.

Chapter 5 examines the individual conduct elements of the crime of aggression, namely ‘the planning, preparation, initiation or execution, by a person in a position effectively to exercise control over or to direct the political or military action of a State’. It considers the extent to which this language makes the crime of aggression a ‘leadership’ crime.Also examined is the individual contribution that must be made by an accused in order to reach a conclusion that an individual has ‘committed’ a crime of aggression, in particular the meaning of the terms ‘planning’, ‘preparation’, ‘initiation’, and ‘execution’, as well as the relevant mental elements. The interaction of the leadership requirement with Rome Statute provisions relating to superior orders and the responsibility of commanders and other superiors is discussed, as is the relevance of the defences of mistake of fact and mistake of law. Finally, the chapter considers the different modes of liability that attract individual criminal responsibility under Article 25(3) of the Rome Statute and whether it is theoretically possible for a leader to order, aid, abet, or attempt a crime of aggression.

In the previous chapter, I explained that we may need to reconsider familiar formulations of fundamental principles when we apply them in new contexts. In this chapter, I ask how we might even embark on such evaluations. A traditional and commendable scholarly reflex is that we must ‘ground’ our analysis in certain and self-evident bedrock. I will show the infeasibility of this search for secure moral foundations.

I suggest a non-foundational approach, using a coherentist method: we do the best we can do with the available clues and arguments. The clues include patterns of practice, normative arguments, and casuistically-tested considered judgments. We can work with ‘mid-level principles’ to carry out fruitful analytical and normative work.

The coherentist approach accepts that our principles are human constructs, that our starting points are contingent, and that we have no guarantees of ‘correctness’. Discussion of fundamental principles is not a matter of ethical computations; it is a conversation. It is a human conversation, a fallible conversation, and nonetheless an important conversation. I also argue that coherentism offers the best explanatory and justificatory account of the method used in most criminal law theory. In other words, it is the best theory of criminal law theory.

The primary source of law before the Court is the Statute itself and the principal subsidiary instruments, the Elements of Crimes and the Rules of Procedure and Evidence. The Court may also refer to relevant rules of international law, notably those of international humanitarian law and international human rights law. Article 25 of the Statute sets out the various forms of participation in crimes starting with direct perpetration but also including ordering and forms of complicity and attempt. Article 28 defines so-called command or superior responsibility, by which an individual may be held responsible for crimes perpetrated by subordinates. The Court cannot prosecute an individual who was under 18 at the time of the crime. Statutory limitation of crimes within the Court’s jurisdiction is prohibited. There is a presumption that all crimes subject to the Court’s jurisdiction require proof of intent and knowledge. Several defences are codified: diminished mental capacity, voluntary intoxication, self-defence, duress and necessity, mistake of law and mistake of fact and, under limited circumstances, superior orders.