Its title notwithstanding, this is not just a highly specialized treatise for criminologists. Gambetta proposes an answer to what one might call Plato’s problem. Early in the book he quotes Socrates asking Thrasymachus: Is it not it unthinkable that “a city, or an army, or a band of robbers and thieves, or any other company which pursues some unjust end in common, would be able to effect anything if they were unjust to one another?” Indeed, is not the normativist explanation of social order, at least in this minimalist version, simply irrefutable? Are such “just” orientations not indispensable, at least within the group, because even those who want to ignore the rules of the wider society can only cooperate if they trust each other?

Gambetta wants to show that this is not the case. For this purpose, he develops a theory of action-coordinating signs that crucially, does not start with the idea of the arbitrary signifier. Instead of assuming the standard case to be one where the relationship between signifier and signified is purely arbitrary, Gambetta starts from the observation that social coordination is often based on signs which seem to prove what they signify, and that even “conventional” signs are often buttressed by signs that seem to have direct evidential value. Accordingly, he draws attention to a specific type of social action – “communicative actions designed at once to inform and to give credibility to the information” (p. xiii). The central idea of his book is that these signs reduce uncertainty, and thus can make cooperation possible even where no trust exists. Gambetta frames his argument in rational choice terms, presupposing conscious calculation on the part of the agent who emits the signal – “I focus only on acts that are intended to be signals” (p. xvi) – as well as on the part of the receiver, who is assumed to calculate whether the signal would be too costly for an agent who is only faking it.

The structuring effect of uncertainty on criminal action was already the subject of Gambetta’s important book on the Sicilian mafia. However, as his new book shows, among criminal enterprises the mafia comes comparatively close to being a textbook-style formal organization. Hence a majority of the case studies from which Gambetta develops his signalling concept concern types of criminal activity that are not supported by this kind of institutionalization, and thus are marked by a higher degree of uncertainty; their environments usually lack coordination-supporting elements that sociological explanations often assume to be permanent features of the social world. For instance, the expectations on which cooperation is based are mainly tied to individuals who, moreover, may regularly be unavailable for cooperation because of prison sentences, tend to have shorter life spans because of their line of business, and are professional liars.

The first type of signal that becomes important here is one that (much like the signals described by the biological signalling theory from which Gambetta draws his inspiration) reveals the agent to be willing and able to perform the activity that is relevant for criminal cooperation. Here, Gambetta partly reintegrates familiar arguments on the role of reputations into a larger theoretical framework. In a case study on prison inmates, he demonstrates (against the still too common practice of treating “violence” and “communication” as simple opposites) how acts of seemingly meaningless violence – as well as acts of deliberate self-harm – may be explainable as conscious attempts to develop a reputation.

However, a central point of Gambetta’s book is that reducing uncertainty by building a stable reputation – often thought to be the standard solution for this kind of dilemma – can only work where uncertainty is not too high. On the one hand, this solution presupposes that such images can “travel through time” (p. 195); criminals, though, are likely to operate in an environment lacking “the conditions that make having a good reputation worthwhile and effective – easy diffusion of reliable information, easy re-identification of previous partners, stability, and long-lived firms” (p. 40). Gambetta shows how taking this into account helps to explain variations, e.g., concerning the level of actual violence necessary to maintain a reputation. Thus, mafia members can most of the time resort to conventional signals that traditionally suggest mafia membership, and only rarely have to back this up by signals that directly prove their capacity for violence. However, even within prisons (which are still comparatively stable environments), the higher the inmate turnover in a given location, the more violence, and the more deliberate self-harm, that even rational inmates may be inclined to produce. On the other hand, building the reputation of being a reliable and trustworthy partner in crime (i.e., somebody who will cooperate even when he has the opportunity to cheat) may be generally impossible since, as Gambetta emphatically points out, there really is no honour among thieves.

Due to these difficulties, a quite different type of signal becomes relevant. Here, Gambetta builds on the work of Thomas Schelling and Jon Elster demonstrating the action-enabling effects of constraints: What finally guarantees cooperation without trust are not signals revealing capacities for action, but signals of incapacities; cooperation is guaranteed because the participants can prove that they would not have the possibility to defect even if they wanted to. One important instance of this is conspicuously displayed incompetence: Selling protection is easier for mafiosi who can credibly show that they would not be able to run the business they are offering to protect (so that there seems to be less of a threat of them trying to take over this business). The same mechanism may, as Gambetta points out, explain the surprising fact that some academics almost gleefully display their lack of academic competence: this may be part of an attempt to qualify as a reliable member of an academic exchange network; by demonstrating their substantial incompetence, they show in a credible way that they (even though they are not trust-inspiring individuals) will have to “repay their debts” because they have no exit option from the network.

Gambetta’s book proves that this concept is indeed highly enlightening: It elucidates ways in which cooperation without trust can become possible; and it suggests a way of explaining puzzling types of behaviour as communicative acts meant to reduce uncertainty. As seen above, it offers “rational actor” explanations for types of behaviour that could be regarded simply as products of a psychiatric illness (like deliberate self-mutilation) or of a formative cultural tradition. (If mafia members behave very much as mafia lore would lead us to expect, this may not be because they remain, unthinkingly, in the grasp of their cultural tradition, but rather because they believe that by acting this way, they can credibly demonstrate their membership status to outsiders, which should usually increase their willingness to cooperate.) Moreover, signals that are not entirely the products of rational calculation are also taken into account; what matters, according to Gambetta, is not the “motive that leads to the production of a signal”, but “whether the act is displayed or otherwise advertised” (p. 128). This enables him to bring out the importance of mixed cases, like that of the genuinely insane prison inmate who repeatedly mutilates himself and then learns the strategic value of drawing attention to his own behaviour.

Still, the question remains whether the possibilities offered by Gambetta’s basic idea – the concept of explaining social order as a product of signals with evidential value – can be exhausted by this rational choice formulation, with its exclusive focus on signs that are strategically displayed and reflexively interpreted, and that are performed in a context where action is not guided by any institutionalized norms whatsoever.

The strong rationality assumption seems to be contradicted by Gambetta’s own examples. On the one hand, they show that social coordination can also be stabilized by signals that are not intentionally conveyed. In his account of self-mutilation in prison, he mentions that, while some such acts are performed strategically, others result from anxiety, and are also understood by other inmates as signals of anxiety. Here Gambetta reports the results of a study according to which “‘genuine’ self-harmers, namely those who through deliberate self-harm express their desperation with prison conditions [...], were more likely to be bullied, whereas ‘manipulative’ self-harmers were more likely to be left alone” (p. 131). Thus, although these signs of weakness are not voluntarily “sent”, they, too, reduce uncertainty by revealing a specific distribution of capacities and incapacities, and therefore contribute to the emergence and stability of an order of asymmetric cooperation. More generally, all kinds of emotional expressions, whether intentionally displayed or not, can have signalling effects. (This point is made in Robert Frank’s book on the “strategic role of the emotions”;Footnote ¹ Gambetta cites the book but does not discuss this argument.) Gambetta proposes that signs which are not intentionally conveyed should not be called signals (p. xv); but such a purely terminological solution does not address the substance of the problem.

On the other hand, Gambetta mentions signals whose effects on social coordination are not mediated by reflexive interpretations. In a chapter on nicknames as signals, he sets out to explain playful forms of abuse among young men in Southern Italy. After rejecting a number of different explanations, he concludes: “[I]t would be a stretch to attribute such uses to an instrumental motive. Unintentionally, though, the ritual tests the solidity of friendship [...]. It is the failure of playful informality to be accepted or reciprocated that reveals its social value. When it engenders a negative response, this brings about a switch from innocent banter to strategic interaction” (p. 248). Pointing out this unintended effect may not explain the stability of this practice (no feedback mechanism is given); still, it suggests the importance of signals that accomplish their social effects not by reducing an uncertainty that is already felt by the agents but rather by preventing such an uncertainty to be felt in the first place (a course of events that fits better into the pragmatist concept of reflexivity as a product of disruptions than into a conventional ‘rational actor’ model taking reflexivity as a given). These signals stabilize trust rather than reflexive expectations; it is only the non-appearance of these signals that makes agents switch into the mode of rational reflection and strategic interaction.

So there seem to be four types of signalling constellations: “Sending” as well as “receiving” of signals can be performed with or without reflection. Gambetta’s book provides a detailed analysis of one of these types. Even where the sphere of illegal economic action is concerned, however, the order-building processes based on signs with evidential value cannot, apparently, be explained by this type alone; using a more varied typology of action would seem to be a precondition for grasping all the relevant mechanisms.Footnote ² At any rate, biological signalling theory – the starting point of Gambetta’s argument – obviously does not assume all signals to be reflectively sent and/or interpreted, either.

There is at least one other important point where the more general ambition of a theory of coordination by signs with evidential value comes into conflict with Gambetta’s rational choice formulation. At the beginning, Gambetta calls “underworld communication”, rather dramatically, a “test case that allows us to see human interactions at their rawest, to lift the veil that civilizing mores and institutions spread over our daily lives” (p. xi); this seems to imply that social coordination is generally based on the mechanisms described here, with criminal coordination only an extreme case helping us to better observe them. However, Gambetta does not really try to sustain such an argument. He certainly establishes that for a “band of robbers”, mutual trust is not indispensable. Yet most of the time, he clearly opposes the “underworld” and “the legal world” (e.g., p. 176), treating the former as a contrasting case to “normal” social coordination. Now, even if restricted to the analysis of this contrasting case, his book would have a theoretical import going beyond the subject of coordination among criminals: It still could help to understand more precisely the character and the extent of the problems solved by legal institutions (and probably, more generally, by social constellations which enable people to trust each other).

Nevertheless, such a self-limitation would be regrettable, since signs with evidential value can also have a cooperation-enabling effect in other types of social contexts. Even where norms have been institutionalized and most actors tend to follow these norms, it can often be uncertain by what kind of action the norm is fulfilled in a given situation; even more so if the relevant normative order results from a compromise among competing principles of justification (as is so often the case). These difficulties can also be resolved by communicative acts that owe their effects to their evidential value. (This is what Boltanski and Thévenot argue;Footnote ³ they, too, develop a concept of social communication that does not take the arbitrary signifier as its paradigm, and that is not exclusively focussed on verbal communication.) Here, too, it becomes apparent that such signs are not only important in cases where coordination is hampered by fundamental distrust. Of course, from the vantage point of rational choice theory, the subject of coordination under conditions of distrust is especially attractive, since the assumption that all agents always act reflexively is especially plausible for social constellations where trust has been severely disrupted. Still, integrating the mechanisms described in Gambetta’s book into a more general explanatory framework seems to be possible only by going beyond the rational choice framework.