What does assumption mean?
An assumption is a statement or belief that is accepted as true without proof or verification. It is one of the most useful words in analytical thinking because so much of our reasoning quietly depends on things we never bother to confirm: plans rest on assumptions about prices, weather, other people's intentions, and the stability of the world around us. When those foundations turn out to be wrong, the consequences can be dramatic — which is why phrases like 'questioning your assumptions' and 'built on a false assumption' are staples of business, science, and everyday argument. Beyond this dominant sense, assumption also describes the formal act of taking up a position or responsibility, as in 'the assumption of power', and it names a major Christian feast commemorating the Virgin Mary's being taken into heaven. Derived from Latin assumere, meaning 'to take up or adopt', the word carries no inherent negativity — but in casual use, accusing someone of 'making assumptions' usually implies they should have known better than to take things on trust.
nounA thing that is accepted as true or as certain to happen, without proof; the act of taking on or beginning a role, duty, or position.
- Something accepted as true or likely to happen without proof or confirmation.
- The act of taking on or entering into a role, responsibility, office, or obligation (e.g. the assumption of power).
- (Christianity) The bodily taking up of the Virgin Mary into heaven, celebrated in the Feast of the Assumption.
"The plan rests on the assumption that interest rates will remain stable."
"Her entire argument collapsed once its hidden assumptions were exposed."
"The vice-president's assumption of office was swift and orderly after the resignation."
"Millions of pilgrims gather each August for the Feast of the Assumption."
The plural is standard and common, especially when referring to multiple underlying beliefs in an argument or analysis.
"The report challenges several long-held assumptions about consumer behaviour."
The word 'assumption' literally means 'to take up' — from Latin assumere — which is why we speak of assuming the presidency: you're not guessing, you're lifting the office onto your own shoulders.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of assumption
Assumption comes from Latin assumere, formed from ad- ('toward') plus sumere ('to take'), originally meaning 'to take up' or 'to adopt'. It entered English via Old French in the Middle Ages, initially carrying strong religious weight through the doctrine of the Assumption of Mary. By the sixteenth century it had developed its broader sense of taking something for granted, alongside its use for the taking-on of offices and duties. It shares its root sumere with words such as consume, resume, presume, and sumptuous.
Related word forms
How assumption is actually used
Neutral to slightly formal register, common in academic, business, and analytical writing. In logic and mathematics, 'assumption' is a technical term for a proposition taken as given. The phrase 'making an assumption' often carries a mildly critical connotation, implying someone has jumped to a conclusion without checking facts.
Easily confused with assumption
A presumption is a belief taken for granted with somewhat stronger justification or legal standing, while an assumption is something accepted without any verification at all.
A premise is a stated proposition used explicitly as the basis of an argument, whereas an assumption is often unstated and implicit.