In his 1786 essay on the pantheism controversy, ‘What Does It Mean to Orient Oneself in Thinking?’, Kant implies that ‘the maxim of reason's self-preservation [Selbsterhaltung]’ is reason's first principle for orienting itself in thinking supersensible objects. But Kant does not clearly explain what the maxim or principle of reason's self-preservation is and how it fits into his larger project of critical philosophy. Nor does the secondary literature. This article reconstructs Kant's discussion of the principle of reason's self-preservation in ‘What Does It Mean to Orient Oneself in Thinking?’ It suggests that this principle is best understood as the discipline of pure reason. The principle of reason's self-preservation performs the same methodological function that Kant assigns to the discipline of pure reason. This principle establishes the rule of law in reason and subjects reason to its own laws. In so doing, it prevents reason's dialectical errors and also grounds reason's faith (Vernunftglaube), which in turn systematically conditions the practical use of reason.