back sb/sth up
phrasal verb.phrasal verb. to support someone or something by agreeing with them or saying they are telling the truth.
phrasal verb. to provide support or corroboration for a person, claim, or theory; to validate the truth or reliability of an assertion.
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.
- support
- confirm
- corroborate
- vouch for
- Particles
- up
- Separability
- optional
- Pattern
- back + object + up
the object can be a person (support) or a statement/claim (corroboration).
distinguish this sense from the computing sense (making a copy of data) and the physical sense (moving a vehicle backwards); all three are common.
He backed up to me in the meeting.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.
Last updated April 24, 2026