back up
3 meanings
move backwards a short way
What does "back up" mean in this sense?
Examples
- Could you back the car up a little? I can't open the gate.
- She backed up slowly into the narrow parking space.
- The truck is too close to the wall — back it up a few metres.
How to use it
Used without an object when it is clear from the situation who or what is moving backwards.
Back up slowly — there's a wall behind you.
When the object is a short noun phrase, it often goes between 'back' and 'up'.
Can you back the car up a little? I need to get past.
With pronouns like 'it' or 'her', the pronoun must go between 'back' and 'up'.
The truck is too close to the fence — back it up a few metres.
Often followed by a direction or destination to say where the vehicle is going.
She backed up into the driveway and turned off the engine.
Common Collocations
Common Mistakes
When you use a pronoun like 'it', you must place it between 'back' and 'up'. Putting the pronoun after 'up' is not correct.
'Back out' means to reverse all the way out of a specific space, like a driveway. 'Back up' just means to move backwards a short distance and does not suggest leaving a place completely.
Usage
This phrasal verb is more common in American English for reversing a vehicle; British speakers often prefer 'reverse'. It can also be used for people moving backwards on foot, not just vehicles.
support something or help make it happen
Sense 2: What does "back sth up" mean?
Examples
- Politicians often fail to back up their words with actions.
- She made a bold claim but couldn't back it up with any evidence.
- The new findings have been backed up by several independent studies.
How to use it
The most common pattern — use it when you have a claim or argument that needs to be supported with evidence or action.
You need to back up your argument before the meeting.
When the object is a pronoun, it must go between 'back' and 'up' — this is not optional.
He said the product was the best on the market, but he couldn't back it up.
Use 'with' to introduce the material that provides the support — this is one of the most natural and frequent structures.
The journalist backed up her story with documents and interviews.
The passive form works well when the focus is on the claim or theory being supported rather than who is doing the supporting.
The health benefits described in the report are backed up by years of research.
This phrasal verb is very common in negative constructions, highlighting a gap between what someone says and the evidence they can provide.
The company made big promises but failed to back them up with any real investment.
Common Collocations
Common Mistakes
When the object is a pronoun like 'it' or 'them', it must go between 'back' and 'up'. Placing it after 'up' is incorrect.
'Back up' can also mean to make a copy of digital files, which is a completely different meaning. Make sure your object is a claim, argument, or statement — not a file or device.
Usage
This phrasal verb is neutral in register and works in both everyday speech and formal writing. The pattern 'back up X with Y' (e.g. 'back up your claims with evidence') is especially common and useful to learn.
support what someone says with proof or evidence
Sense 3: What does "back sb/sth up" mean?
Examples
- You have to back up your accusations with solid evidence.
- She made some bold claims, but she couldn't back them up.
- His theory was backed up by years of scientific research.
How to use it
The most common pattern — use 'back up' with an abstract noun like a claim, theory, accusation, or story as the direct object.
You need to back up your argument before submitting the paper.
When replacing the object with a pronoun, it must go between 'back' and 'up', never after 'up'.
Those are serious allegations — can you back them up?
Use 'with' to specify the type of proof being offered to support the claim.
She backed up her findings with data from three separate studies.
The passive form is natural and common, especially when describing whether something is or isn't supported by evidence.
The government's position was not backed up by independent research.
Often used in negative or conditional statements to express that a claim should not be made without supporting proof.
You can't publish something like that without backing it up.
Common Collocations
Common Mistakes
When using a pronoun as the object, it must go between 'back' and 'up'. Placing it after 'up' is ungrammatical in English.
When the object is a person, 'back up' means to take their side or defend them — not to provide evidence. Make sure your object is a claim, argument, or statement, not a person.
'Back up' in this sense is not normally used in continuous tenses. Stick to simple or perfect tenses, or use infinitive constructions.
Usage
This phrasal verb is neutral in register and works in both formal writing and everyday conversation. It is very commonly followed by 'with' to introduce the supporting evidence: 'You need to back up your claims with facts.'
Frequently Asked Questions
Can 'back up' be used for people, not just cars?
Yes! You can use 'back up' when a person or a group of people moves backwards on foot. For example, if someone is standing too close, you might say 'Back up, please — give her some space.' It is very natural in this situation.
Is 'back up' British or American English?
'Back up' is used in both, but it is more common in American English for talking about reversing a vehicle. British speakers often prefer 'reverse' in driving situations, especially in formal or instructional contexts. However, British speakers will understand 'back up' with no problem.
Does 'back up' always mean moving backwards?
No — 'back up' has other meanings too, such as supporting someone or making a copy of computer files. This page covers only the movement meaning. The context usually makes it clear: if a vehicle or person is moving backwards, this is the sense being used.
Can I say 'The car was backed up into the space'?
This is very unusual. With this movement meaning, we almost always use active sentences with the driver or vehicle as the subject, for example 'She backed the car up into the space' or 'The car backed up into the space.' A passive form sounds unnatural here.
Does 'back up' always mean support? I've heard it used in other ways.
No — 'back up' has several different meanings in English, such as reversing a vehicle or saving a copy of computer files. This page covers only the 'support a claim or argument' meaning. The object is your best clue: if it's a claim, theory, or statement, you're looking at this sense.
What kinds of things can I 'back up'?
In this sense, you back up claims, arguments, statements, theories, accusations, promises, and decisions — anything that is a position or assertion that needs support. You cannot use this sense with a person as the object or with data and files.
Can I use 'back up' in formal writing, like an essay?
Yes — 'back up' is neutral in register and is perfectly natural in both everyday conversation and formal or academic writing. You might write 'back up your argument with evidence' in an essay without sounding too casual.
What does the 'with' mean in 'back up your claim with evidence'?
The word 'with' introduces the supporting material — the facts, data, or actions that make the claim credible. Think of the structure as 'back up [what you're supporting] with [what you're using to support it]'. This pattern is very common and worth practising.
Is 'backed up by' common in news articles or academic texts?
Yes, the passive form 'backed up by' is very common in both journalism and academic writing, where writers want to focus on the claim or theory being supported rather than on a specific person supporting it. For example: 'These conclusions are backed up by recent data.'
Does 'back up' always mean to provide evidence for something?
No — 'back up' has several different meanings depending on the context. This particular sense is specifically about establishing something as valid through proof or evidence. Context usually makes the meaning clear: if the object is a claim, theory, or argument, this is the sense being used.
Can I use 'back up' in academic writing?
Yes, absolutely. This sense of 'back up' is neutral in tone and works well in academic writing, especially in structures like 'back up your argument with evidence' or in the passive form 'the hypothesis was not backed up by the data'. It is a natural and widely accepted choice in formal contexts.
What kinds of things can be 'backed up' in this sense?
The object is typically something abstract and propositional — a claim, argument, theory, accusation, allegation, statement, story, or finding. You are essentially providing proof that it is true or valid. You would not use this sense when the object is a person or a computer file.
Can 'back up' be used without specifying what evidence is provided?
Yes. You can say 'you need to back that up' or 'she couldn't back up her claims' without mentioning what evidence is missing. The 'with + evidence' part is optional — it simply adds detail about the type of support being used.
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