certitudo

Certitudo is a Latin noun (feminine: certitudo) meaning certainty, assurance, or confidence. The term derives from certus, meaning sure or certain, and is used in classical and later Latin to denote a state of unshakable conviction or trust, in knowledge, in decisions, or in a relationship.

In philosophy and theology, certitudo can refer to the interior assurance by which a person accepts propositions or embraces a belief, as distinct from mere opinion or guesswork. In medieval and Catholic theological writings, certitudo fidei (certainty of faith) is the degree of conviction accorded to divine truths, often linked to grace and to the authority of revelation. The concept is discussed in relation to epistemic certainty, natural philosophy, and faith, as a measure of confidence that a proposition is true or binding.

Outside theology, certitudo appears in general prose to express personal confidence or security in a course of action, a promise, or a person— "firmness of mind" or "steadfastness." The term is common in Latin dictionaries and academic Latin texts but rarely used in modern English except in translations or quotations.

In modern scholarship, certitudo is treated as a historical linguistic concept illustrating how Latin speakers distinguished different forms of conviction: cognitive certainty, moral assurance, and trust. It sits alongside related notions such as fides (faith) and fiducia (trust).