The Science of Deception examines how ideas about deception, and especially commercial deception, influenced the origins of American psychology as a scientific discipline. It will interest legal historians on several fronts: as an analysis of professionalization in the late nineteenth century, as a discussion of how important legal dilemmas can shape the course of scientific inquiry, and as an investigation into the ways that scientific ideas about human behavior influence legal decision making.

Pettit's point of departure is the nineteenth century American fascination with deceit, a byproduct of industrialization, urbanization, and national economic integration. Amid a quickly evolving economy rife with anonymous transactions and informational asymmetries, Americans had good reason to ponder both “the deceitful self”—from the occasional shader of truth to the outright confidence man—and the “deceivable self”, both P. T. Barnum's “sucker born every minute,” and less credulous individuals, who nonetheless still occasionally found themselves taken for a ride. Legal considerations only heightened the demand for ways to understand duplicity and to unmask it. American legal culture embraced the principle of caveat emptor, and typically viewed fraud allegations as sour grapes from individuals whose greed had led them astray. Pettit persuasively portrays P. T. Barnum's various promotions as playing on the common recognition that one needed to be able to look sharp, and the equally widespread uncertainty over exactly what that entailed in a rapidly changing society.

The first American psychologists, Pettit contends, similarly framed much of their research and public discourse around the problem of economic illusion. Through a variety of laboratory experiments, many late nineteenth century scientists came to see the vulnerability to deception as a function of constraints on human cognition, a “law of economy” that led people to rely on various cues in sizing up the persons and economic situations that they encountered. (Although Pettit eschews comparisons with more recent developments in cognitive psychology and behavioral economics, this line of argument anticipated current thinking about the use of heuristics to filter the onslaught of information in modern societies.) Other scholars attempted to study the practices of grifters through a deceptive form of ethnography, seeking to understand the “criminal classes through a disguised immersion into their milieu” (39).

Like many new professions, academic psychologists also expended considerable effort to expose the deceptions of various cranks and popular imitators, in their case, the spiritualists, mesmerists, and psychics who slaked popular thirst for knowledge about the occult and access to nonrational means of comprehension. But to obtain the secrets of their competitors, Pettit demonstrates, these scholars of human thinking and behavior soon discovered that they had to learn the tricks of stage magicians and emulate the era's private detectives. The exposure of charlatans required all manner of deceptive misdirection, and although leading psychologists consistently lambasted the fakirs as unscrupulous money grubbers and portrayed themselves as resolute seekers of truth, their research findings increasingly suggested the difficulties in achieving truly disinterested assessments of facts.

By the early twentieth century, leading psychologists sought to consolidate their professional authority by bringing their expertise to bear on expanding governmental regulation of the truthfulness of commercial speech, such as the Federal Trade Commission's investigations of unfair methods of competition. Scientists such as Hugo Munsterberg and Richard Paynter developed tests that measured the likelihood of a consumer being fooled by a brand knockoff or cleverly imitative trademark; along with sympathetic legal scholars, they tried to convince courts to accept their assessments as legally definitive markers of illegitimate marketing tactics. Through a close examination of appellate cases, Pettit shows that the Progressive era judiciary proved unwilling to cede the power to determine what counted as illegal trickery, but encouraged by the legal teams of large-scale corporations who wished to protect their brands, the courts did adopt significant exceptions to caveat emptor, premised on a vision of an “unwary purchaser.”

This development signaled the diffusion of modern psychological thinking, as did two coterminous innovations in criminal investigation: the uneven reliance on the new technology of the lie detector, and application of psychotherapy to the assessment of criminal behavior, as with the identification of psychopaths. In perhaps the strongest section of the book, Pettit concludes by tracing how deception became a bedrock element of psychological testing in academic laboratories and corporate personnel departments. In part because of their engagement with the search for legal standards of behavior and motivation, psychologists spent a great deal of time confronting the problem of the strategic subject, who might respond to straightforward queries with lies, evasions, or self-deception. To overcome that problem, psychologists tried to study behavior through ingenious research designs that hid the point of experiments; but this maneuver only raised new and complex ethical dilemmas about transparency and consent. By the 1930s, most psychologists viewed deception as an inevitable aspect of social life, something to manage rather than hope to eliminate.

Pettit's research rests primarily on close readings of psychological literature, the private papers of key psychologists and criminologists, and pivotal appellate cases. Therefore, it remains an open question how quickly psychological mindsets seeped into quotidian criminal and regulatory enforcement. Pettit also misses some potentially rich comparative contexts, such as the way that nineteenth century fertilizer and grain adulteration shaped the emergence of professional chemistry; or the impact of psychological thinking on the early twentieth century business establishment's war on fraud. This is, nonetheless, a fine piece of intellectual and cultural analysis that speaks to the value of integrating the history of legal values with that of scientific ideas and practices.