What's the difference between

Why would you do that?


Why did you do that?

I always saw the sentence 'why would you do that' while watching movies. Why they prefer to use the word 'would'?

  • 1
    If it's not a conditional usage (in response to say 'If I bought a Hum-Rover, I'd sell it again within two years', then it's just a pragmatic hedging usage ('Why would you do that', meaning the same as 'Why did you do that', but less in-your-face). Commented Aug 24, 2016 at 15:56
  • I suspect there as American v British divide here. I recall someone harassing Tom Cruise (throwing water over him or something) and he said "why would you do that?" which in British English sounds really odd because "would" seems to imply something counterfactual. I would have said "why did you do that?". If you are interested in American English, it might be worth saying so for clarity. Commented Jan 7, 2021 at 22:26

2 Answers 2


With "Why would you do that?" you're questioning the other person's motivations, which implies that a) it was deliberate and b) they might do it again.

With "Why did you do that?", you're asking about the decisions and circumstances around that past event.

Let's say you broke an ornament (which you hate) by accident, and your partner says "Why would you do that?", they're implying you did it on purpose. You might say "I didn't mean to, it was an accident!". You're replying to the implication that it was deliberate.

If they say "Why did you do that?", you might say "I tripped on one of the kids toys and knocked it off the shelf." Here you're just saying what happened.

EDIT: this answer assumes that the questioner is asking about something that has happened. If the thing being discussed is hypothetical then as @EdwinAshworth points out in his comment, it takes on a less accusatory tone: because nothing has actually happened, there's no question of deliberate vs accidental for example: you're simply asking about someone's motivation or opinions.

  • 1
    This strikes me as muddled. The basic aspect that would carries in such an interrogative is one of possibility or choice. This may be accompanied by disapproval or dismay -- "Why would you do [or have done] such a thing?" -- when you question a contemplated [or chosen] course of action. It may express the possibilities in response to a conditional (per EA). But it may be judgment neutral: "A: I think I'll turn left at the next corner." B. Why would you do that?
    – deadrat
    Commented Aug 24, 2016 at 17:33

'Why would you do that?' implies that the speaker thinks there is not a good reason for having done it. In contrast, 'Why did you do that?' implies that the speaker acknowledges that there might have been a reason for doing it and is just asking which reason was actually the cause.

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