English Reference

Phrasal verb

back up

Irregular verb

Forms

Infinitive

back up

Past

backed up

Past participle

backed up

Definition

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

phrasal verb. 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.”

Examples

simple

“He always backs up his friends during an argument.”

contextual

“When the manager accused him of being late, his colleagues backed him up by explaining the train delay.”

complex

“The witness's testimony failed to back up the defendant's claims, leading the jury to question the validity of the entire alibi.”

Usage

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.

Pitfall

I will back up him.

I will back him up.

When the object is a pronoun, it must be placed between the verb and the particle.

Phrasal verb

Particles

up

Separability

optional

Pattern

back + up + object

Synonyms

supportstand byconfirmcorroborate

Antonyms

contradictundermine

Grammar

Phrasal verbs (introduction)

This entry

Exam level
CambridgeCambridgeCambridge English QualificationsThe exam suite from Cambridge University Press & Assessment, from A1 Movers up to C2 Proficiency. The benchmark names double as CEFR labels.B2 FirstIELTSIELTSInternational English Language Testing SystemThe 0–9 band test co-owned by the British Council, IDP, and Cambridge. Used for university entry, work, and migration.5.5–6.5TOEFL iBTTOEFL iBTTest of English as a Foreign Language, Internet-Based TestETS's academic English test, the standard route for US university admissions. Scored 0–120, with a 1–6 scale since 2026.1–6 scale: 4.0–4.572–94TOEICTOEICTest of English for International CommunicationETS's workplace English test, big in Japan and Korea. Listening & Reading scores 10–990 and tops out at C1.785–944
Frequency
Very common
Level
B2 · Upper Intermediate
Updated

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English Reference