common knowledge

IPA/kˈɒmən nˈɒlɪdʒ/
IPA/kˈɑːmən nˈɑːlɪdʒ/

common knowledge — idiom

1. something that is known to most or all members of a group or community — so wide

1.idiomB2
Definition

something that is known to most or all members of a group or community — so widely accepted that people consider it unnecessary to explain or prove.

Example

It is common knowledge among the villagers that the old well has been dry for decades.

it + be + common knowledge + among [group] + that-clause

The company's financial troubles became common knowledge when the annual report was leaked.

became common knowledge

Common collocations
  • common knowledge that
  • common knowledge among
  • common knowledge in
  • common knowledge within
  • be common knowledge
  • become common knowledge
  • treat something as common knowledge
Synonyms
  • well-known fact

    slightly more formal; often used in academic or journalistic writing

  • general knowledge

    broader in scope — can refer to things learned through education, not just everyday awareness

  • public knowledge

    emphasises availability to the general public rather than a specific community

  • open secret

    implies that something is known despite not being officially acknowledged; slightly informal

  • widely known fact

    more explicit about scope; can sound more formal

Antonyms
  • secret

    information deliberately kept from others

  • mystery

    implies something puzzling or unexplained, not merely unknown

  • inside information

    known only to a select few with special access

  • rumour

    unverified information; may or may not be true

Grammar Patterns

it + be + common knowledge + that-clause

something + be + common knowledge + (among/in/within) + group

Usage Note

Can range from 'known by everyone in a group' to 'known by most members of a group'. The strength depends on context. Frequently used predicatively with a that-clause ('It is common knowledge that…'). Cannot be preceded by an article ('a common knowledge') because it is an uncountable noun phrase.

Common Mistakes

It is a common knowledge that the moon orbits the Earth.
It is common knowledge that the moon orbits the Earth.
'common knowledge' is uncountable and does not take an indefinite article.
Common knowledge tells us that smoking is bad for health.
It is common knowledge that smoking is bad for health.
'common knowledge' is not an agent; it cannot 'tell' us things.
The common knowledge among engineers is that the bridge needs repairs.
It is common knowledge among engineers that the bridge needs repairs.
'common knowledge' typically avoids the definite article even when a prepositional phrase follows.

Synonym discussion

Sense: idiom/1

All four phrases refer to information that many people are aware of, but they differ in scope and connotation. 'General knowledge' covers broad factual information that an educated person is expected to know (e.g., 'the capital of France is Paris') and is often taught in schools. 'Well-known fact' is more selective — it flags a single piece of information as widely recognised without implying a whole body of shared knowledge. 'Public knowledge' stresses that nothing has been hidden from the general public; it is commonly used in legal or journalistic contexts ('the affair became public knowledge'). 'Open secret' adds the nuance that something is known despite being officially denied or concealed ('his resignation was an open secret'). For example: 'That vitamins help prevent scurvy is general knowledge among sailors, while the exact dosage needed is less well known.' 'The merger was an open secret on Wall Street long before the press release.'

general knowledgewell-known factpublic knowledge ↗open secret ↗

Etymology

LatinOld EnglishEnglish

'Common' comes from the Latin 'communis' ('shared by all'), and 'knowledge' comes from the Old English 'cnāwan' ('to know'). The two words have been used together as a fixed phrase since at least the 1500s to refer to facts or truths that are understood by all members of a community without needing explanation.