Marcus Holmes opens his important and well-written book on face-to-face diplomacy with a fundamental question: Why do leaders and diplomats ascribe so much importance to face-to-face meetings? Holmes argues that face-to-face diplomacy shapes outcomes and helps foster cooperation. He develops a theoretical answer as to why this is the case based in social neuroscience, the interdisciplinary field dedicated to how biological systems shape social behavior and processes. Using process tracing and counterfactual analysis, Holmes seeks to isolate the causal effect of face-to-face encounters. He shows that when political leaders and diplomats engage in face-to-face interactions they generally understand their counterparts’ intentions better than if they had only interacted from afar. After reading this original book, I am convinced that face-to-face diplomacy matters and that it can reduce uncertainty about state intentions, but I am less persuaded that the mirror system in the brain plays such a crucial role in this process. I will get to why—and why I still think this book is an absolute must-read—after a summary of the argument.

Face-to-Face Diplomacy is structured in seven chapters. In chapter 1, Holmes explains that face-to-face diplomacy is usually disregarded in scholarship as “cheap talk” (p. 3), because structural phenomena are often seen as more important for shaping outcomes in world politics. However, Holmes argues that neuroscience isolates the “unique signaling mechanism that allows leaders to escape the problem of intentions, and thus the security dilemma, by communicating their intentions to each other at a very high degree of specificity” (p. 5).

Chapter 2 develops this theoretical argument further by linking “the problem of intention” to social neuroscience. The argument is that when leaders and diplomats meet face to face, they activate the brain’s mirroring system, enabling neural synchronizations between individuals, which in turn gives them more direct access to the intentions of others. The mirroring system picks up on small facial changes and subtle shifts in the emotional states of others. This system is also able to detect lies and deceit and thus to evaluate with a high degree of accuracy whether the other is speaking the truth. This, in short, explains why leaders put so much emphasis on face-to-face meetings.

The four subsequent chapters put the argument to work empirically. Chapter 3 zooms in on the interactions between Mikhail Gorbachev and Ronald Reagan, where both sides attempted to reassure the other of their benign, defensively minded intentions. Holmes suggests that it was the face-to-face interaction rather than assessments in the respective capitals of the two superpowers that helped the two parties come to an understanding.

Chapter 4 examines how the Bush administration realized that the Soviet Union would accept a unified Germany in NATO despite Gorbachev’s public protest. The chapter shows that this realization came about in face-to-face meetings held not only between Bush and Gorbachev but ultimately also between lower-level diplomats across Europe. As such, the chapter demonstrates how the many and costly face-to-face meetings changed outcomes and, indeed, that Germany might not have been united without it.

Chapter 5 examines the 1978–79 Camp David Accords between Israel and Egypt, mediated by Jimmy Carter. Holmes emphasizes Carter’s role in face-to-face deliberations: the president worked with each party individually to understand their intentions and arbitrate an agreement based on that understanding.

Chapter 6 tackles the problem of deception and what Holmes calls “the most well-known moment of deception in modern diplomatic history and it occurred when Neville Chamberlain was looking in Adolf Hitler’s eyes in a face-to-face encounter” (p. 18). Holmes suggests that a key reason why Chamberlain could not detect that Hitler was lying was Chamberlain’s “clinical narcissism and hubris syndrome” (p. 230).

Chapter 7 sums up the book and discusses how face-to-face diplomacy transcends the problem of the security dilemma at the interpersonal level and thus increases the amount of certainty, rather than uncertainty, in international relations.

As should be clear from this summary, the book embarks on the methodologically difficult task of combining insights from biological (especially neural) mechanisms with micro-sociological and IR concepts. As such, it is impressive in its contributions to our understanding of diplomacy and face-to-face interactions. These contributions also raise important questions about the benefits and pitfalls of importing biological mechanisms into the study of international relations.

First, does the empirical material offer enough of an indication of what goes on inside people’s heads to sustain the argument that it is the mirror system doing the work? Holmes acknowledges that he is analyzing an “unobservable casual mechanism” (p. 241). The book effectively employs process tracing and counterfactuals, drawing on a range of sources, but as Holmes acknowledges throughout the work, we do not have the kind of empirical data on these face-to-face interactions that would be needed to fully assess whether it is indeed the mirror system that is at work. I would add that even if we had better data—for example, from scanning diplomats’ brains during interactions—brain science still lacks an understanding “of cerebral functions to infer mental processes from neural activations,” as scholars have noted (Gayannée Kedia, Lasana Harris, Gert-Jan Lelieveld and Lotte van Dillen, “From the Brain to the Field: The Applications of Social Neuroscience to Economics, Health and Law,” Brain Sciences 7(8), 2017). Indeed, in international relations, as Holmes also writes, it is difficult to extrapolate the results of laboratory neuroscience studies to real-life situations. Even if IR scholars did experiments that would simulate real-life events, they would still be far from the complexity of world politics. Moreover, we would still not know exactly how (or if) biological mechanisms produced particular social effects.

Second, what is the role of human reflexivity? Neuroscience relies on the idea that it is important to explain how and why individuals are able to decipher intentions. But perhaps the more important thing is not whether leaders and diplomats are able to do so, but that they (and others) think that they are able to ascertain intentionality in others. Indeed, Holmes writes, “If there is fundamental uncertainty in the international system, which leads to a problem of intention understanding, practitioners often belie that uncertainty and act as if they are certain about the other” (p. 244, emphasis in the original). This “as if” might be enough to explain the overall puzzle of why practitioners insist that tête-à-tête interactions matter. Indeed, if face-to-face diplomacy is a social practice with its own shared expectations, including that such meetings have value, it could still shape outcomes—with or without the brain’s mirror system. In short, the book highlights the need for further research on the relationship between the reflective and intuitive aspects of face-to-face interactions.

Third, can we really understand state intentions as “individual intentions since it is individuals who create them” (p. 28)? Certainly, we should not underestimate the role of individual decision makers, especially not in the cases that Holmes examine, but today, state intentions are hardly individual: they are based on group decisions and institutional and historical legacies. Moreover, individual leaders often lack the time and resources to develop clear intentions. Instead, as Holmes also emphasizes, top-level or summit diplomacy is often a staged spectacle, following a detailed playbook, where most of the negotiations are done before the actual face-to-face meeting summit. Thus, Holmes’s argument might be even more relevant to lower-level diplomacy where continuous face-to-face interactions are more common.

Although they challenge the book’s argument, these questions also illustrate Holmes’s thought-provoking contribution to our understanding of diplomacy. Face-to-Face Diplomacy deserves to be read not just by students of diplomacy but also by any scholar of international relations interested in the microdynamics of world politics.