assumption

assumption — noun

1. an idea you treat as correct in your reasoning, even though nobody has shown evi

1.nounC1
Definition

an idea you treat as correct in your reasoning, even though nobody has shown evidence for it.

Example

Priya planned the picnic on the assumption that Saturday would be sunny.

on the assumption that + clause

The detective questioned every assumption the local police had made about the missing keys.

verb + assumption (question / challenge)

Common collocations
  • make an assumption
  • challenge an assumption
  • question an assumption
  • false assumption
  • safe assumption
  • underlying assumption
  • on the assumption that
  • rest on an assumption
Synonyms
  • presumption

    more formal; suggests stronger confidence in the belief

  • supposition

    neutral; emphasises that the idea is unconfirmed

  • premise

    used in arguments and logic; the idea you build reasoning on

Antonyms
  • fact

    something proven, not just believed

  • proof

    evidence that removes the need for assumption

Grammar Patterns

assumption + that-clause

on the assumption that...

Usage Note

Frequently followed by a that-clause or used in the fixed phrases 'on the assumption that' and 'under the assumption that'. Common verbs with this sense include 'make', 'question', 'challenge', and 'rest on'.

Common Mistakes

I have an assumption to do my homework first.
I plan to do my homework first.
'assumption' is a belief you accept without proof, not an intention or task.
My assumption about him being lazy was true.
My assumption that he was lazy turned out to be true.
follow 'assumption' with a that-clause, not 'about + -ing'.

2. the moment when someone formally begins to hold a job, role, or duty, especially

2.nounC2
Definition

the moment when someone formally begins to hold a job, role, or duty, especially one that carries authority.

Example

Dr. Park's assumption of the role of head teacher surprised many staff at Lincoln High.

assumption of + role / position

The new mayor marked his assumption of office with a speech in the city park.

assumption of office (formal collocation)

Common collocations
  • assumption of office
  • assumption of power
  • assumption of command
  • assumption of responsibility
  • assumption of the throne
  • assumption of control
  • assumption of duties
Synonyms
  • takeover

    more common in business; suggests gaining control of a company or group

  • acceptance

    focuses on agreeing to a duty rather than the moment of starting it

Antonyms
  • resignation

    leaving a role rather than starting one

  • abdication

    formal giving up of a high office, especially a throne

Grammar Patterns

assumption of + noun

Usage Note

Almost always followed by 'of + noun' (office, power, command, control, the throne, responsibility). Sounds formal or ceremonial; in everyday speech use 'taking on' or 'taking over' instead. Distinguish from sense 1: this sense is about an event of starting a role, not about a belief.

Common Mistakes

After his assumption as president, he gave a speech.
After his assumption of the presidency, he gave a speech.
use 'of + noun', not 'as'.
She made an assumption of the manager job last week.
She took on the manager's job last week.
in everyday English, 'take on' or 'take over' is more natural than 'make an assumption of'.

Word family

  • assume
    verbB2
  • assumed
    adjectiveC1
  • assuming
    conjunctionB2
  • presumption
    nounC2
  • presume
    verbC1

Synonym discussion

Sense: noun/1

All five words name an idea accepted before evidence is in, but they differ in tone and use. 'Assumption' is the everyday choice and feels neutral — you simply take something for granted, often without realising it. 'Presumption' sounds more formal and suggests stronger confidence, sometimes even arrogance, as in 'the presumption of innocence' in court. 'Supposition' highlights that the idea is tentative, useful when guessing aloud: 'It's just a supposition, but maybe she missed the train.' 'Premise' belongs to argument and logic — it is the starting belief you build a conclusion on. 'Hypothesis' belongs to science: an assumption you actually plan to test. So you 'make an assumption', 'argue from a premise', and 'test a hypothesis'.

assumption ↗presumptionsuppositionpremise ↗hypothesis ↗

Common collocations

Nouns

  • assumption of power
  • assumption of office
  • assumption of responsibility

Adverbs

Phrases

  • make an assumption
  • challenge an assumption
  • question an assumption
  • rest on an assumption
  • work on the assumption that

Prepositions

  • on the assumption that
  • under the assumption that
  • assumption about
  • assumption of

Etymology

LatinOld FrenchMiddle EnglishEnglish

From Latin 'assumere', meaning 'to take to oneself', built from 'ad-' ('to') and 'sumere' ('to take'). The word entered English through Old French in the 14th century. Its earliest English uses were religious, naming the church festival celebrating Mary being taken up to heaven. Over time the meaning broadened: by the 1600s English speakers used it for 'taking on' a role or duty, and later for any idea a person 'takes' as true without proof. Today both threads survive — sense 1 (a belief taken up) and sense 2 (a position taken up).