This chapter discusses Alexis de Tocqueville’s nuanced criticism of rationalism. Being a modern liberal and critical friend of democracy, his political science finds that Enlightenment political science, which aims at wholesale social engineering, is actually an unscientific and partial ideology. Rationalism espoused by French philosophes and physiocrats depends on assuming ever more control over people’s lives, destroying politics properly so-called. Tocqueville recommends keeping some distance between politics and philosophy, for the sake of both, and ultimately for our sake. We discern that the relationship between politics and philosophy can best be described as an uneasy friendship. Reason and liberty should benefit each other mutually and reciprocally, but they cannot do so if they are in a relationship where one dominates the other in however well-meaning a fashion, or if it is imagined that their unity is too easily attained and secured. Political freedom requires virtue, and virtue requires reason, but reason is best developed when human beings are given the freedom to develop their own minds and character in association with others. Although reason and liberty are inherently complementary, politics dominated by an uncritical veneration of reason, especially an Enlightenment conception of reason that is simultaneously excessive and deficient, undermines virtue and freedom alike.