Can the present tense be used in the past tense to refer to something that always happens or to something that hasn't happened yet? [duplicate]
With "reported speech" the important thing is to explain the information, not the words, to your listener. The information needs to be true and make sense to your listener now. The OP's sentence is slightly complicated by the fact that it uses a question. Let's look at two declarative sentences:
Consider the following direct speech:
- It is against the law to steal.
Now, if stealing is against the law now then we can use either of the following sentences to report this:
Mary was told that it was against the law to steal.
Mary was told that it is against the law to steal.
This is because Mary was told that generally stealing is not allowed. This situation was true when Mary was told it, and so sentence (1) is correct. If Mary was told that it is generally against the law to steal, then sentence (2) is correct as well. The information Mary was giving was not intended to just be true about that particular time.
Which choice we use though, may be important. If we are trying to show that something is still true now, for example, we will probably use sentence (2). If we are trying to describe a story in the past or a situation in the past we will use sentence (1). Here is an example where it might be important to use sentence (2).
Suppose you want to tell somebody that you have a particular policy about something, and that you have checked this with your boss. Because we are interested in what the situation is now we will expect you to say:
- The Director said that this is our policy.
Now if you say:
- The Director said that this was our policy.
Then this might sound as if your policy has changed now, but it used to be your policy. This implication will be stronger because we expect the sentence to say is our policy, so we might think there is a special reason for you to change the tense here.
Of course both sentences are true and both sentences are grammatical, but in this situation, it might be better to say it is our policy, just because the listener will not be able to misunderstand the sentence.
The Original Poster's sentence:
- Why do people cry
This situation is the same as the ones above. The speaker was asking about why people cry in general. We can portray it as a question about the general situation at the time of speaking or as a general situation from the current perspective. Remember, it is the information that is important, not the words. We can use either of the following:
- She asked why people cry.
- She asked why people cried.
You don't have to, but you would usually say, "My teacher asked why people cried." It's called reported speech. Normally with reported speech we revert to the past tense. You could say it the other way, but that's not typical. The only reason you would would be if you had a reason to believe that you would be misunderstood. People don't misunderstand this though. People are used to hearing reported speech in the past tense.
Backshifting is not a simple matter of "everything is backshifted." Oftentimes, backshifting will change the meaning in a way that is not appropriate. This came up in a BBC newscast about Ghadaffi. Ghadaffi made the statement My people love me. When his statement was reported by the BBC, the news agency had two choices: a direct quote or reported speech. For reported speech, the newspaper would have written:
"Ghadaffi said that his people loved him."
For quoted speech they would have reported:
"Ghaddafi said "My people love me.""
The BBC decided to report it as:
Ghadaffi said that his people loved him.
In this case, the backshift significantly changed the meaning and undermined Ghadaffi--the intent of the reporting, which did not go unnoticed by savvy political commentators. A non-native speaker might look at that sentence and say "See, no one loves Ghadaffi anymore."
This is also done when reporting things said on the telephone. For example, "Peter is on his way." or "Peter will be five minutes late." I feel that generally statements like these will be quoted and not backshifted. Or the verb tense will be changed to make the statements current for the listener.
What did Peter say? He said / says he's on his way.
What did Peter say? He said / says he is going to be five minutes late.
In both of those options the speaker has the choice of backshifting, however the backshift would open up the possibility of further questions. "Peter said he was on his way." could be countered with: "Well, is he still coming or did he get delayed?" I think for most native speakers this is invisible and when asked, most will say "I'm not sure what I would say." or "I'm not sure why I said it that way." Or if asked what they would say (and I have asked many teachers this) will say "No, I always backshift."
For your example I would say, "My teacher asked me why people cry." It's certainly not wrong to say "My teacher asked me why people cried." but in my opinion the meaning changes. My advice on matters like these is to pick one style and use it consistently, or if you are able to remember this while speaking make a choice.