Locke stresses the power of custom in shaping opinion and behavior, though this aspect of his thought has been underappreciated. Recognizing its importance raises critical issues, particularly the relation between custom and reason and the role of authoritative custom in supporting political and social power. Locke explains in detail the various psychological and sociological mechanisms by which the power of custom is manifested; but he nonetheless consistently and emphatically rejects its authority. Instead, Locke is a champion of the authority of reason. Because custom is powerful, but reason is authoritative, Locke attempts to enlist the power of custom in the service of reason and of reasonable politics, and because custom is powerful and its impact unavoidable, individual intellectual independence cannot mean being without cultural prejudices. At best, it means the ability to gain some critical distance from them. These observations place Locke's relation to the Enlightenment in a new perspective. © 2012 University of Notre Dame.