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Which is correct?

  • To back up data.
  • To back data up.

The context is the following: He was careful enough to perform tests and [back up data | back data up] to avoid any problems.

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up vote 10 down vote accepted

Back up data is by far the most common, (referencing two Google searches (1780000 results vs. 18200) and Ngrams), and sounds the most natural. This is because back up, though written as two words in verb form, is spoken (and thought of) as one word. To split the "verb" up and put something in between (e.g. data) would be to confuse the meaning of the sentence for most people.

He was careful enough to perform tests and back up data to avoid any problems.

Backup as one word is a noun/adjective, and is not applicable as a verb.

The backup software on this computer is ancient.

The backup runs from 12 AM to 1 AM every night.

Edited to say that I wholeheartedly agree with @tdhsmith's comment:

...while keeping the "verb" whole is generally more readable with wordier objects, most native speakers must split it when using a pronoun. For example, "I back it up every night" is correct to me but "I back up it every night" feels very wrong. [See below for the entire comment]

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Does anyone have a good resource on phrasal verbs here? That would be useful. Anyway I think you should add that while keeping the "verb" whole is generally more readable with wordier objects, most native speakers must split it when using a pronoun. For example, "I back it up every night" is correct to me but "I back up it every night" feels very wrong. Or at least it does when associating the right (phrasal) meaning. If I said "I back up it every night" where I am talking about my car and it is my steep driveway, that'd be fine. – tdhsmith Sep 8 '11 at 19:29
When you say "back up it", talking about backing your car up your driveway, is "up" a preposition or part of a phrasal verb? (Or both, which I think might be what is going on here. I don't think anybody ever says "back up up the driveway", although they might say "back up into the garage".) – Peter Shor Sep 8 '11 at 20:27
+1 @Peter Didn't think of that. I would think that it is either, depending on context. It's a preposition when there is a complete prepositional phrase (e.g. I backed the car up the driveway). It's part of the verb when there is no prep. phrase (e.g. I backed up the car). It's the difference between falling down and falling down the hill. So in back up it, the meaning of up depends on what it is referring to. If the car, then it's part of the verb (back up); if the driveway, then it's part of the prep. phrase and therefore a preposition (up the driveway). – Daniel Sep 8 '11 at 20:37
BTW, that last comment was 500 chars on the dot. I want to add that when the up is "part of the verb", I think it's technically an adverb. – Daniel Sep 8 '11 at 20:41
@drɱ65 δ: Adverbial up distinguishing it from other back compounds, such as off, down, away, out? They don't seem much like normal adverbs (slowly, very, quite) to me. I think all you can say is that the pair is a phrasal verb (or just a simple verb, if you drop the intervening space). Certainly it's an area where attempting to apply rigorous terminology is likely to end in tears and/or foot-stamping. – FumbleFingers Sep 8 '11 at 22:33

Normally, back up as a verb is seen as a compound form that shouldn't be broken, so OP's first example is the standard phrasing. But all credit to @lettuce_pants for pointing out that you can (must, in fact) split the words when using a pronoun - for example, "I back it up every night".

That compound (technically, a phrasal verb) is often collapsed into the single word backup (almost always, when used as a noun/adjective as in backup data, backup plans, etc.).

OP's second example is far from unknown - quotated "back your data up" gets over 500,000 hits on Google. But there are 2.5M for "back up your data", and 1.8M for "backup your data".

So whilst I personally don't think it's meaningful to talk about "correct" usage here, the safest, easiest option is to always use backup. If you're confident you always know when you're using it as a verb, insert the space (but no other words apart from pronouns) in that context. Then no-one will ever be able to find fault, no matter how pedantic they are.

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I will always find fault with the use of "backup" as a verb. – phoog Jan 4 '12 at 23:26

"back up data" is probably better, if you consider back up to be one term/word, ie. "back up", "back-up", "backup".

The only problem is that "backup data" could refer to the data itself rather than the operation. eg. "The backup data is on tape" rather than "we backup data onto tape"

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That's why I thought "back data up" could be better, as a way of making sure the term is used as a verb.. In my context, to see the term as a noun is kind of weird because you end up "performing backup data", which doesn't mean anything. – Shawn Sep 8 '11 at 18:31
@Shawn: Most native speakers should be capable of knowing whether "backup" is functioning as a verb or not in any given sentence. Or even phrase, as in your examples where you precede it with the word "to" so we know it's a verb. It might be harder to say whether it's a noun or an adjective in the backup disc, but that doesn't matter - it's not a verb, so the space is unwanted. I must say I think hyphenating it is very unusual though, and I would never advise using that. – FumbleFingers Sep 8 '11 at 22:21

Backup data is what you have after you back up your data before putting it back up on the shelf. The only time you back your data up is when your data needs confirmation and you give it.

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I would almost +1, because this is amusing, but I don't see that splitting "back up" up depends on the sense. – phoog Jan 4 '12 at 23:29

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