For all the recent discoveries of behavioral psychology and experimental economics, the spirit of homo economicus still dominates the contemporary disciplines of economics, political science, and sociology. Turning back to the earliest chapters of political economy, however, reveals that pioneering figures such as Francis Bacon, Thomas Hobbes, and Adam Smith were hardly apostles of economic rationality as they are often portrayed in influential narratives of the development of the social sciences. As we will see, while all three of these thinkers can plausibly be read as endorsing “rationality,” they were also well aware of the systematic irrationality of human conduct, including a remarkable number of the cognitive biases later “discovered” by contemporary behavioral economists. Building on these insights I offer modest suggestions for how these thinkers, properly understood, might carry the behavioral revolution in different directions than those heretofore suggested.