# back sb/sth up

CEFR B2 · Phrasal verb

Source: https://englishreference.com/word/back-sb-sth-up
Updated: 2026-04-24

## Definition

to support someone or something by agreeing with them or saying they are telling the truth.

For teachers: to provide support or corroboration for a person, claim, or theory; to validate the truth or reliability of an assertion.

## Examples

- My sister will back me up if I tell my parents.
- The witness was able to back up the driver's story with a video from her phone.
- The lead researcher presented several peer-reviewed studies to back up his controversial hypothesis during the international conference.

## Pitfalls

- Not "He backed up to me in the meeting." but "He backed me up in the meeting." — when used for support, the object usually sits between the verb and the particle if it is a pronoun.

## Usage notes

- the object can be a person (support) or a statement/claim (corroboration).
- Teaching tip: distinguish this sense from the computing sense (making a copy of data) and the physical sense (moving a vehicle backwards); all three are common.

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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.