Using past tense when referencing a still-true fact

In the sentence: "I didn't know she had a son,"

Can I say "I didn't know she has a son" instead, because he is a teenager now?

Or are both correct?

Answer

If she currently has a son, then you can use either version #1 or #2:

• 1.) "I didn't know [(that) she has a son]."




• 2.) "I didn't know [(that) she had a son]."

For that situation, where she currently has a son, the #2 version happens to use a backshift preterite. (Note that "preterite" is the same thing as a "past-tense verb"). As to which version is preferable, well, that depends: which one do you prefer? That is, which one sounds better to your ear?

One of the reasons why a subordinate clause -- like your "(that) she has a son" -- can be backshifted into "(that) she had a son" is that the matrix clause is headed by a preterite (the verb "didn't").

Backshifting in a subordinate clause can occur when either one of the following conditions is true:

• A.) The tense of the matrix clause is a type of past-tense.




• B.) The time of the matrix clause situation is in the past time sphere.

Sometimes, depending on the purpose of the sentence, there can be a preference for either the non-backshifted version or for the backshifted version. Sometimes the non-backshifted version might be considered to be "much more widely appropriate" than the backshifted version. Sometimes the backshifted version is obligatory.

NOTE: There's a common misconception that a present-tense verb being used in its timeless sense (or other related uses) cannot be backshifted. That is untrue, as backshifting is still generally available. For instance, in the older 1985 reference grammar by Quirk et al., A Comprehensive Grammar of the English Language, section 14.31, page 1027:

Here are other examples where present forms may be retained in indirect speech:

• Their teacher had told them that the earth moves around the sun. -- [11]

. . .

In all these sentences, past forms may also be used, by optional application of the backshift rule. Sentence [11] has the simple present in its timeless use, . . .

And so, according to Quirk et al., the following backshifted version (to correspond to [11]) is also acceptable:

• Their teacher had told them that the earth moved around the sun.

Here are some related posts, on the topic of backshifting:

(Some of the material in this post has been borrowed from those two related posts.)