When to Use "Did You Know" Instead of "Do You Know"
Friday May 27th 2016
Why do we say "did you know" rather than "do you know"? — D.M., Pakistan
The phrase "did you know" is used when you are asking someone if they know a fact, and you already know that fact. For example, you might say "Did you know that the blue whale is the largest mammal?" where "the blue whale is the largest mammal" is a fact that you know. An appropriate answer would be "no" if the person you are asking did not already know that before you asked your question, or "yes" if they already knew that fact. Once you've asked the question, they know! "Did you know" can be used to ask about any kind of fact. You are basically saying, "I know this, and I want to know if you know this too." Below are some common questions people might ask:
Did you know I used to be a marathon runner?
Did you know Jeff's sister just got married?
Did you know there was a parade last weekend?
Did you know the Smith's are selling their house?
In each of these examples, the speaker wants to know if the listener already knew the given information before the question was asked. The speaker already knows the given information.
The phrase "do you know" is usually used when you are trying to find out information that you do not know. For example, you might say "Do you know where Patty's office is?" The person you are asking will usually give you the information you want, if they can: "Patty's office is the third one on the right." Below are some common questions people might ask:
Do you know how to replace a headlight bulb in your car?
Do you know how much a trip to Cancún costs?
Do you know where the nearest mall is?
Do you know if the Smith's are selling their house?
In each of these examples, the speaker wants to know some piece of information, and they hope the listener can tell them. The speaker does not know the information being asked for.
The main difference is that you use "did you know" when you already know the information that follows and you use "do you know" when you do not know the information that follows, but you want to know.