This chapter introduces the central ideas in Darwin’s Expression, poses the main interpretive questions that scholars have raised, and outlines my answers to those questions. Why does Darwin analyze expressions in terms of heritable habits, recalling Lamarck’s debunked theory of evolution, when his own theory of natural selection provides a superior alternative? My answer is that Darwin embraces Hartley’s associationist theory of mind, which posits habit as the basis of thought. I claim that multiple puzzling features of Expression are resolved once we view Darwin as an associationist philosopher.

This chapter examines Darwin’s taxonomy of emotions. I show that nineteenth-century associationists were divided on whether emotion categories exist in nature or are conventional. Herbert Spencer argues that emotion categories exist in nature, anticipating modern basic emotions theory. Thomas Brown argues that emotion categories are conventional, anticipating modern psychological constructionism. I show that Darwin sides with Brown and regards emotion categories as conventional. This finding is surprising, since Darwin is often viewed as a precursor to modern basic emotions theory, which adopts the opposite view.

This chapter argues that Darwin’s philosophical theory of emotion has been forgotten due to paradigm shifts in biology, psychology, and philosophy. These shifts have caused researchers to neglect associationist theories of emotions, including Darwin’s contributions to this school of thought. Having explained why Darwin’s philosophy was forgotten, I conclude by explaining why it should be remembered, given its relevance for contemporary emotions research.

This chapter traces the development of Darwin’s theory of emotion and expression from 1838 to 1872, emphasizing his many engagements with associationist philosophers. I demonstrate that all three of Darwin’s principles of expression are derived from the works of associationist philosophers, especially David Hartley, Erasmus Darwin, Herbert Spencer, and Alexander Bain.

The Introduction presents the main theses of this book: that Charles Darwin developed a philosophical theory of emotion, inspired by his reading of several associationist philosophers; that Darwin denied that emotional expressions evolved as social signals, designed to reveal emotions to others; and that Darwin’s theory of emotion has more in common with modern constructionist theories than with modern basic emotions theories, which often claim Darwin as their inspiration.

This chapter surveys associationist theories of emotion leading up to Darwin’s Expression. These theories analyze emotions as sequences of thoughts, feelings, and actions, linked together by principles of association. Thomas Hobbes contributes to this tradition the idea that emotions can be analyzed as “trains of thoughts.” John Locke contributes the idea that these trains are connected by the “association of ideas.” David Hume contributes the idea that association can occur via contiguity, resemblance, or cause and effect. David Hartley puts these ideas together to present the first full-fledged associationist theory of mind and emotion. Harley’s ideas are developed further by Joseph Priestley, Erasmus Darwin (Charles’s grandfather), Thomas Brown, James Mill, Alexander Bain, and Herbert Spencer, among others. This tradition in the philosophy of emotion has never before been described or analyzed.

This chapter examines Darwin’s analysis of emotional expression. It is widely accepted that Darwin wrote Expression to refute Sir Charles Bell’s theory that God created humans with special muscles to express their emotions. However, scholars have overlooked the fact that Bell developed his theory to refute Erasmus Darwin’s associationist analysis of emotional expression, inspired by David Hartley, and that Charles Darwin defends his grandfather’s analysis against Bell’s objections. I demonstrate that Charles’s defense of Erasmus’s associationist theory, which denies that expressions occur for the sake of communicating emotions, explains Charles’s puzzling reluctance to claim that expressions evolved to serve as signals in communication.

Rumsfeld's comments – which came in the middle of a news briefing regarding the possible presence of weapons of mass destruction in Iraq – were largely treated with derision at the time, even winning a ‘Foot in Mouth’ award from the UK Plain English Campaign for the ‘most baffling comment by a public figure’. The phrasing is, perhaps, tortuous, and the structure confusing. But (remarkably enough) the basic idea that Rumsfeld is trying to convey is an important one, and one that we will explore throughout this chapter. Knowing and not knowing are generally taken to be straightforward, binary categories: we know or do not know a particular fact. But in practice these categories have texture and nuance. As Rumsfeld says, there are different ways of not-knowing, and, as we will see in Chapter 7 in particular, knowledge itself can be fragile and contestable. In this chapter we explore some of this fragility, looking at what happens to technoscientific knowledge in times of disaster or crisis, as well as the ways in which both knowledge and non-knowledge are constructed through the intermingling of scientific, social, and political processes. We therefore examine the kinds of unknowing that Rumsfeld describes. How do we come to know some things, know that we don't know others, and are entirely ignorant of the existence of others again?

Knowing and not knowing

In the decades since Rumsfeld made his comments the field of ignorance studies has emerged. Its basic premise is that ignorance is not simply emptiness or lack, but a rich social space that emerges in particular ways and has particular uses. In scientific research, for instance, we know particular things and not others because of funding and scholarly priorities and interests, all of which operate to focus research on specific areas (we continue to be ignorant of, for instance, many aspects of women's health, because standard scientific models are generally male, or of diseases that dominate the South rather than the rich North).

I am writing from what feels like a time of crisis. As I sit in my office in Vienna the COVID-19 pandemic continues to rage, causing everything from cancelled meetings and online teaching to millions of excess deaths across the world. The climate crisis – the onset of changes in the global climate caused by human activity – is beginning to shape weather patterns and the degree to which particular regions of the world are habitable; each year, we see more extreme weather, alongside disasters such as widespread flooding or wildfires. And there are conflicts and clashes at national borders. Two countries over from where I sit in Austria, Russia has invaded Ukraine, and the country is the site of appalling violence as it fights to maintain its sovereignty. This is, however, just one example of forms of nationalistic aggression that are taking place around the world, from Colombia to Afghanistan, which are causing widespread death, destruction, and displacement. Many predict that such conflicts will only increase as climate change reshapes the world's landscapes.

This is not a book about these crises, or the many others that shape our world. It is, however, a book about one thing that these events have in common. In all of these examples, scientific and technical knowledge and expertise are central to how they are understood, managed, and unfold. While they are not only scientific crises or controversies, science and technology are vital aspects of them. To take some examples: I have just read an expert commentary on the war in Ukraine that uses the results from ‘war games’ to discuss possible outcomes of the current situation. These highly technical processes use modelling to try and understand different conflict scenarios, with the results of such games themselves feeding in to political advice and decision making. I have also just carried out a PCR test for COVID-19, a now regular occurrence to check whether I am infected and whether I can safely meet with others. My results will come back in 24 hours: I have become adept both at carrying out the test and reading the results (I have learned what a ‘CT value’ is, for instance).