What does certainty mean?
Certainty is the state of being completely sure — a condition of mind free from doubt in which something is accepted as true, known, or inevitable. It can describe either a psychological state ('She spoke with certainty') or an objectively settled fact ('Taxation is a certainty'). In everyday use it conveys assurance and conviction, but in philosophy and science it carries a stricter meaning: few claims, if any, meet the standard of absolute certainty, so researchers instead speak of degrees of confidence. Common collocations include 'with certainty', 'moral certainty', and 'absolute certainty'. Its natural opposites are uncertainty and doubt. Derived from the adjective 'certain', ultimately rooted in Latin 'certus' (settled, fixed), the word entered English via Old French. Certainty remains a valuable word precisely because it names both what we feel when we are sure and what we rarely fully possess.
The state or quality of being certain; complete freedom from doubt about something.
"He could not say with any certainty when the project would be finished."
In this sense certainty is usually uncountable.
A fact or event that is definitely known or bound to happen; something inevitable.
"Change is one of the few certainties in any organization."
This sense is countable and takes the plural 'certainties'.
The plural applies mainly to the countable sense — established facts or inevitable events — not to the abstract state of being sure, which is normally uncountable.
"Death and taxes are the classic certainties of life."
Benjamin Franklin famously declared that nothing in life is certain except death and taxes — and even he was borrowing an idea already centuries old.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of certainty
Certainty comes from the Latin adjective 'certus', meaning fixed, settled, or determined, which passed into Old French as 'certain' before entering English in the medieval period. The noun 'certainty' developed from the adjective, alongside the related verb 'ascertain'. Other words sharing this Latin root include 'concern' and 'discern', which derive from related Latin verbs of sifting and distinguishing. The parallel form 'certitude' arrived later, borrowed more directly from Latin 'certitudo'.
Related word forms
How certainty is actually used
Certainty is slightly more formal than 'sureness' and more concrete than 'confidence': one may have confidence in a plan while still lacking certainty of its success. It commonly appears in philosophical and scientific contexts, where claims are graded by degrees of certainty rather than treated as absolute. The plural form 'certainties' typically refers to established facts or inevitable events rather than to states of mind.
Easily confused with certainty
Certainty is the general state of being sure about something, while certitude refers specifically to a firm, often unshakeable conviction, sometimes held without objective proof.
Certainty concerns confidence in knowledge or outcomes, whereas security concerns freedom from danger or threat.