Chapter 5 commences by retracing how, beginning in Nuremberg, the reasonable person entered the battlefield in the form of the reasonable military commander. Subsequently the chapter explores two challenges that confront the concept of the reasonable person on the battlefield and beyond. The first challenge consists in the fact that it is easier to empathise with people who are close to us. In the theatre of war, this raises the question whether the reasonable person, when acting as the reasonable military commander, can meaningfully balance the interests of civilians on opposite sides. The second challenge relates to the fact that it is more difficult for powerful people such as military commanders (or judges) to take the perspective of others and to empathise with them.

The introduction begins by acknowledging that the reasonable person is not just a powerful legal concept but also a legendary legal figure that is little understood. It explains briefly how the concept operates in practice and introduces the book’s core argument concerning empathetic perspective taking. Outlining the structure of the book, the introduction then proceeds to addressing the limitations of the analysis and the unique challenge of setting out to write a biography of the reasonable person without either caricaturising or fetishising it.

Chapter 3 focuses on the application of the reasonable person in the nineteenth and twentieth centuries. The chapter begins by considering why the reasonable person is frequently placed on means of public transport. It argues that the reasonable person’s presence on the omnibus means that others can see it and that the reasonable person itself sees others. The chapter then considers whether the standard of the reasonable person was meant to be an empirical standard or a standard controlled by the courts. It does so by asking whether the idea was that one could actually encounter the reasonable person on the Clapham omnibus. Contrasting the concept of the reasonable person with the concept of the average human person proposed by the Belgian sociologist and astronomer Adolphe Quetelet, the chapter establishes that the reasonable person was meant to be a court-controlled standard. Finally, the chapter shows how the standard has historically been construed exclusively in male terms. It addresses the discriminatory potential of the standard and acknowledges that the reasonable person concept has often been applied in a manner that excludes anyone who does not share the characteristics of the male, white, middle-aged judge who applies the standard.

Chapter 2 focuses on the emergence of the modern concept of the reasonable person in nineteenth-century Britain. It argues that this development resulted from the legal and economic needs of the industrial revolution and was informed by the metaphysics of the Scottish sentimental Enlightenment. The chapter’s point of departure is the case known as Blyth v The Company of Proprietors of the Birmingham Waterworks, one of the first cases to discuss explicitly modern law’s reasonable person. Distinguishing between a rational Enlightenment and a sentimental Enlightenment, the chapter then shows that the underlying rationale of the reasonable person relies heavily on the sentimental Enlightenment, namely on David Hume’s and Adam Smith’s thought on the importance of empathy, judgement making in relation to the feelings of others, the incomplete understanding of morality that can be gained from objective reason, and the importance of a human common sense. The third section explains how the industrial revolution and the sentimental Enlightenment influenced the life of Baron Alderson, the judge who oversaw Mr Blyth’s case against the Birmingham Waterworks.

This chapter explores the reasonable person’s encounter with entities that possess artificial intelligence (AI). A discussion of this encounter is particularly important, since it has been argued that the advent of AI will lead to the demise of the reasonable person. The first section focuses on the ability of the reasonable person standard to assess the behaviour of machines or algorithms that act on behalf of humans and lack autonomous decision-making capacities. The second section considers proposals to replace the reasonable person standard with a reasonable robot or reasonable AI standard. The section also asks to what extent the reasonable person standard can be used to assess the behaviour of autonomous digital agents that act autonomously. The third section discusses contemporary proposals to subjectivise law through big data, in a manner that would dispense with the need for a reasonable person standard, since everyone would be measured with reference to their own personal standard.

This chapter considers how and in what contexts the reasonable person standard was applied by the selected colonial courts of the British Empire. The key question is whether the reasonable person imported from England remained English in substance – whether it continued to resemble a man on the Clapham omnibus – or the courts tailored the standard to the specific circumstances before them. As the first section shows, there are many cases in which the reasonable person was equated with an Englishman. This suggests that the standard was static in nature. However, the second section of the chapter complicates this conclusion by introducing numerous cases and settings in which the standard was adapted to specific, local contexts – sometimes so successfully that local variants of it developed. Drawing together the first two sections, the final part considers the nexus between a standard’s resemblance to the people to whom it is applied and the authority of law.

This chapter explains that the reasonable person was not the first anthropomorphised legal standard. The idea of model characters can be traced back to the oldest documents of humanity. The chapter introduces three of these ancient ancestors of the reasonable person: the silent person of Egypt (geru maa), the earnest person of Greece (ho spoudaios), and the male head of a family in ancient Rome (paterfamilias). There are many other ancestors of the reasonable person, and at least implicit anthropomorphised standards of behaviour could probably be found in any society at any time. The three concepts here are presented only as examples, and because they form part of one Mediterranean context in which the ancient Egyptians probably influenced the ancient Greeks, who in turn influenced the Romans, whose influence on contemporary European law and on the systems derived from it can still be felt. Each of the three figures introduced in this chapter deserves its own biography and the analysis offered here remains fragmented. Nonetheless, the selected aspects of the lives of the geru maa, of the spoudaios, and of paterfamilias foreshadow many of the questions, tensions, and challenges with which the common law’s reasonable person still struggles today.

The Conclusion argues that the reasonable person possesses an essence that can be traced across time and across the different jurisdictions we encountered. This essence concerns the concept’s fundamental acceptance that ours is always just one perspective among many and that the best way to understand and assess what others think, do and feel is to empathise with those others. Since the standard is not always understood or applied in this manner, the Conclusion offers a restatement of the function and rationale of the common law’s most illustrious character; the aim is to contribute to the realisation of the concept’s potential and to make it easier to identify instances of misuse. The section unfolds in three parts, which correspond to the three steps of judgement making through empathetic perspective taking: the intention to take the reasonable person’s perspective; the assumption of the reasonable person’s perspective; and the making of a judgement by reference to the reasonable person’s perspective. Ultimately the Conclusion argues that the concept of the reasonable person has significant potential to facilitate the making of tolerant and humane judgements in a diverse, globalised and dynamic society, provided that one remembers that the reasonable person is always someone else.