# back up

CEFR B2 · Phrasal verb

Source: https://englishreference.com/word/back-up
Updated: 2026-10-22

## Definition

to support someone or say that what they are saying is true. You use this when you help someone prove their point.

For teachers: To provide support or evidence for a person or their statement. The verb is optionally separable, though the object must be placed between the verb and particle when it is a pronoun.

## Examples

- He always backs up his friends during an argument.
- When the manager accused him of being late, his colleagues backed him up by explaining the train delay.
- The witness's testimony failed to back up the defendant's claims, leading the jury to question the validity of the entire alibi.

## Pitfalls

- Not "I will back up him." but "I will back him up." — When the object is a pronoun, it must be placed between the verb and the particle.

## Usage notes

- When the object is a pronoun, it must be placed between 'back' and 'up'.
- Teaching tip: Contrast with 'back down' to show how the particle 'up' suggests reinforcement while 'down' suggests retreat.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.