I came across this sentence today in a wait screen for a twitter client:

Did you know that this wait is actually Twitter's fault, not ours?

Is "Did" correct usage in this case? I didn't know it earlier, but I became aware of it as I read it. Hence this seems logically correct. But a "Do you know..." sounds more natural in this case. What tense would be correct in this case?


Generally speaking, you are right that tenses matter. "Do you know Amy?" or "Do you know where I can get a cheap PC?" are grammatically certainly not the same as "Did you know Amy?" or "Did you know where I can get a cheap PC?"

However, the question at hand, "Did you know that this wait is actually Twitter's fault, not ours?", is different from the aforementioned examples in that the intent of the asker is not to get an answer from you, but rather to provide you with a piece of information. What they are actually saying is:

This wait is Twitter's fault, not ours.

That's all. But note how much harsher it sounds. Rephrasing this as a question is simply a more polite way to convey the same information. In short: the question is rhetorical.

As such, theoretically it could be worded in pretty much any way the asker chooses: "Did you know that...", "Do you know that...", "Would you like to know that...", "May we draw your attention to the fact that...", "Would you mind if we mentioned that...", etc. However, out of the multitude of all possible templates the "Did you know that..." one has emerged to be the most popular one. It is extremely common in spoken conversation, and it is now a well-established template for messages displayed during loading times, from KDE to video games. As nohat succinctly puts it in his answer, it's "a pretty standard formula".

Now, as to why the standard formula has become the one that uses the past and not the present tense, I don't know for certain. However, I will point out that the past tense is often used to make things sound (even) more polite. For example, note the difference between saying "I was wondering if" versus "I am wondering if".

  • Oh, and I forgot to mention the "would" vs "will", as in "Would you do this?" which is more polite than "Will you do this?" Nowadays, some might argue that this example is a bit of a stretch, but that's the whole point: it's become so common that many people don't even realize that historically, "would" is just a past-tense form of "will". – RegDwigнt Oct 6 '10 at 9:05

“Did you know…?” is a pretty standard formula for presenting potentially new (usually trivial) information to people. It’s dressing up the presentation of the new information in a question for politeness, which in the context of a real conversation would give the listener an easy opportunity to respond with “No, I didn’t know that—thank you so much for telling me”, or something like that. It’s a polite way to convey information without sounding teacherish, especially if there is a substantial likelihood that the listener already knows that information.

“Do you know…?” would not be a substitution with the same meaning.


I think the "did you know / do you know" usage is not about the event (already passed or about to happen), but more about the intent of the question:

  • "do you know... ?": I don't know, but I hope you do and that you can answer me...
  • "did you know... ?": I already know, but I think you might not know, so I inform you of...

Note, as RegDwight, when a subordinate "that" is involved, the asker knows about what he/she is asking in both cases ("do you know that" or "did you know that").

The difference is then more an enforcement vs. information one:

  • "do you know that ... ?": I do know, but and you should really take that into account
  • "did you know that... ?": I already know, but I think you might not know, so I inform you of..., feel free to ignore it however.

RegDwight's answer(+1) illustrates that is really more about interpreting a usage than determining an precise "correctness"...

  • I don't quite agree that "Do you know...?" implies "I don't know, but I hope you do and that you can answer me". It might imply that when followed by an interrogative, but when followed by a subordinating "that", it implies the exact opposite thing. "Do you know where I can find X?" ⇒ the asker doesn't know where he can find X. "Do you know that it's illegal to do Y?" ⇒ the asker is very much aware that it is illegal. "Do you know how to get there?" or "Do you know Jim?" ⇒ no implication either way, further context is needed. – RegDwigнt Oct 1 '10 at 12:06
  • @RegDwight: I quite agree (and included your comment in my answer). I didn't saw your answer right away. +1 – VonC Oct 1 '10 at 12:29

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