Abstract: LIBERALS OFTEN THINK diversity of belief and its expression should be tolerated in order to respect either individuals or reason and truth themselves. Because they are agnostic about the good for man, they hold that liberty for each to pursue his or her conception of the good in “self-regarding” matters is required, and that practices of toleration are important aspects of this liberty. They also often advocate practices of toleration as means by which reasoned and true beliefs can come to prevail over false beliefs. Each line of thought justifies practices of toleration as means to something which is seen both as logically independent and as of more fundamental value. These familiar lines of thought are not the only possible liberal vindication of toleration. In Kant’s writings toleration is not a derivative value, to be established only when the value of true and reasoned belief and of liberty in self-regarding matters has been established. His arguments for toleration of what he terms “the public use of reason” presuppose neither antecedently given standards of rationality nor that any class of self-regarding individual actions is of special importance. For Kant the importance of (some sorts of) toleration is connected with the very grounding of reason, and so in particular with the grounding of practical reason. His arguments suggest that liberal political thinking can vindicate practices of toleration without commitment either to a strong form of individualism or to the view that we can distinguish “self-regarding” acts, and without claiming that reasoning either has a “transcendent” vindication or is groundless. The themes of toleration and of the grounding of reason are brought together in many Kantian texts. The most important is the Critique of Pure Reason, in particular the section of the Doctrine of Method called “The Discipline of Pure Reason in Respect of its Polemical Employment.” I The same connection is stressed in many other places, including scattered passages in the Second and Third Critiques, in the Logic, and in Religion within the Limits of Reason Alone. A number of shorter essays, including “What Is Enlightenment?” (1784), “What Is Orientation in Thinking?” (1786), “Idea for a Universal History with a Cosmopolitan Purpose” (1784), “The Conflict of the Faculties” (1798), “On the Common Saying ‘This may be True in Theory, but it does not Apply in Practice’ ” (1795), and “Perpetual Peace” (1795),2 appear at first to have much to say about toleration, including the political aspects of toleration, and little about the grounding of reason. Yet here too the themes are often interwoven. The close connections between the short political essays and the central critical writings suggest not only that the essays are part of Kant’s systematic philosophy, and not marginal or occasional pieces, but also perhaps that the entire critical enterprise has a certain political character. If this is the case, it is no accident that the guiding metaphors of The Critique of Pure Reason are political metaphors. If the discussion of reason itself is to proceed in terms of conflicts whose battlefields and strife are scenes of defeat and victory that will give way to a lasting peace only when we have established through legislation such courts, tribunals, and judges as can weigh the issue and give verdict, then it is perhaps not surprising that Kant links his discussions of politics very closely to larger issues about the powers and limits of human reason. However, this is a large and for present purposes somewhat tangential issue.3 The more immediate concern is to see how Kantian arguments link toleration to the very grounding of reason.