Fürwahrhalten, or “holding-to-be-true”, is one of the most controversial concepts in Kant’s epistemology. Rarely mentioned in Kant’s edited works – where it is often used to describe moral faith – Fürwahrhalten has attracted the interest of Kant scholars only in recent years. The essay aims to shed light on some of the main issues that the notion of holding-to-be-true still rises, especially those concerning its origin and its theoretical function in the critical system. The book retraces the stages of Kant’s reflection on this theme, starting from the precritical discussion with the main representatives of the German Enlightenment (Wolff, Knutzen, Baumgarten, Meier, and Crusius) to the definitive formulation of Fürwahrhalten after the publication of the Critique of Pure Reason. The analysis of Kant’s logical corpus has shown that, far from being a marginal concept of critical epistemology, Fürwahrhalten is the core of a systematic theory of certainty, that Kant develops in accordance with his doctrine of modality. This theory represents the arrival point of a long and troubled reflection, that led Kant to deeply rethink most of the traditional themes of eighteenth-century logic