I am not sure if this is the case, but can we use the idiom "set someone up" before there's evidence that X betrayed us, or is it something we can only say after the signs indicate that X betrayed us. In the dictionary, there doesn't seem to be any hint of that implication, but I've never seen it used in a different situation. Is it a synonym of "betray" and can we use it in any situation where we can use the word "betray"?

For example:

A: I don't think he set us up. Why should we believe that?

B: Look outside, there are SWAT people coming in through the fence. Still believe he didn't betray us?

A: Oh, maybe he did set us up.

3 Answers 3


Yes, it's ok to use without knowing if the betrayal has really happened.

I think it's even more common to use that phrase when speculating that a set up might have happened. So, the typical case could be that the speaker doesn't know for certain.

  • And are "set up"and "fake out" interchangeable, both as nouns and verbs? Nov 3, 2019 at 8:41

It definitely can be used in the context of suspicion, speculation, guessing the future etc, like in your case. Thing is it doesn't overlap the meaning of 'betray' 1:1. Specifically, it focuses on arranging a specific situation with specific outcome with the subjects not knowing about it.

One can betray a group, by running away with goods he/she was trusted and leaving them empty-handed (but still safe). One can join the forces of the enemy and start fighting against former allies, still not passing any intelligence on them to the enemy. In general, being disloyal is a betrayal.

Setting someone up, firstly, doesn't necessarily have to be negative. Someone may bribe the jury of a contest to have one of the contestants win - without the contestant knowing. This is setting the contestant up to win.

Then, there is the consequence - a direct effect on the party that was set up - in case it's a betrayal, knowing the betrayed plays a key role: informing the enemy of a hide-out, or a pending transaction or some evidence - or even framing them - producing fake evidence that will get them in trouble. Never mind no prior trust or loyalty is necessary. Two co-workers may hate each other and one will set the other up, arranging a situation (say, sabotaging the work) where the victim is bound to fail, get blamed for the failure and suffer the consequences. Definitely a set-up, but not a betrayal because there was no expectation of loyalty in the first place.


A "set up" is a kind of betrayal, but not a synonym for betrayal.

For example, suppose you cheated on a test at school and told your good friend about it, who then told the teacher. You might consider you friend's action a betrayal -- but it would not be a set up.

In order to be "set up" you would have to have put your trust in someone to carry out some part of a (usually nefarious) plan, but that person turned around and betrayed you for some kind of personal advantage. In other words, it can't be random and it can't be haphazard. The set up has to be part of the plan.

To give a concrete example: in a recent film the two main characters went to a mob boss to borrow money to start a business. The mob boss was supposed to help them bribe the local government to get them the necessary permits, but instead he fixed it so that (after borrowing the money) they were unable to get the permits. He set them up so that he could take over their business, and they would still owe him money.

It is possible to be set up without knowing who set you up. In your example, the two characters could say something like:

Look outside, man! We just got here and already SWAT is coming through the fences? Someone set us up.

By this the speaker is accusing someone of telling the police about them in order to get some advantage, even something as basic as a reduced criminal charges.

This "personal advantage" doesn't have to be financial. It can be as basic as the pleasure of watching an enemy go to jail. Many thriller movies end this way, with the good guy at first set up by the bad guy, but in the end turning the tables so the bad guy is the one who is set up and punished.

Side note: If someone told the police without expecting personal gain, there are other expressions, for example:

someone tipped off the cops!

If they wanted to say that someone trusted told the police, without suggesting it was part of a larger plan, they could say:

someone ratted us out to the cops!

In standard criminal slang, a "rat" or a "snitch" is someone who tells the police about other criminals' plans.

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