Your English: Word grammar: proof

Proof is mainly used as a noun but it can also be used as a suffix. As a noun meaning ‘evidence’, it is followed either by of or that, as in ‘Do you have any proof of identity?’ or  ‘Do you have any proof that this is true?’

Proof can also be used as a standard for measuring the strength of alcoholic drinks and, in particular, strong alcoholic drinks such as vodka or whiskey, as in ‘She bought a bottle of 80% proof whiskey’, with the proof being approximately equivalent to double the percentage of alcohol actually in the drink.

Proof is also used in the term living proof, where it is used to describe an example that shows that something is true, as in ‘She’s living proof of the saying that life begins at fifty’ and, with a similar meaning, in the expression proof positive, as in ‘The incident was proof positive of the need for officers to be armed in dangerous situations’.

Usually used in the plural form, proofs are copies of a book or article that are read and edited before a final version is published. This also gives us the verb proofread, meaning to read a document and correct any mistakes.

Proof also functions as a suffix and is used with certain nouns to describe something that will provide protection against the damaging effects of something else, as in a bulletproof vest or recession-proof shares. Other common examples include waterproof, shockproof, rustproof and fireproof.