Past tense or present tense to describe something that 'happened in the past' but is still true? [duplicate]

I know the past tense carries the past tense in every dependent clause, but referring specifically to places or to things that are eternal, like the Earth, seems a bit weird and therefore we sometimes (I believe incorrectly) say

He didn't know that New Jersey was actually on the East Coast.

Because it still is. Or

He thought the Earth was round.

So is it square now?

Logically speaking, would you consider the use of past tense here a bit confusing in a day-to-day speech in these examples? Would you instinctively opt for using the present tense?

Both tenses are OK, but I believe the past tense is a bit more common: it may be somewhat contrary to logic, but it sounds better. Harmony of tenses (if that's what it's called) is a linguistic phenomenon that is not always very logical.

The clauses that New Jersey was actually in the East Coast and the Earth was round are known in functional grammar as 'projected clauses'. They behave in the same way as clauses that contain what is known in traditional grammar as 'reported speech'. As the authors of the ‘Longman Grammar of Spoken and Written English’ explain:

Simple past tense has a special use in reported speech or thought. The original speech or thoughts may have been in present tense, but past tense is usually used for the reports . . . Notice that the circumstances may still be continuing even though past tense is used (My emphasis).

1.) "Last week, I found out that NASA stands for 'National Aeronautics and Space Administration.'"

or

2.) "Last week, I found out that NASA stood for 'National Aeronautics and Space Administration.'"

Both versions #1 and #2 are acceptable. It's up to you (or your editor) as to which one you want to use. The second version happens to use a backshifted preterite ("stood") in the subordinate clause.

To explain backshifting, it might be easier to use an example.

Assume that Kim has blue eyes, and that Tom knows that. And then Tom tells me,

• "Kim has blue eyes."

Then I can tell you,

• "Tom told me that Kim had blue eyes."

which has backshifting. Or I can choose to not use backshifting,

• "Tom told me that Kim has blue eyes."

Both versions are fine. Note that Kim's eye color is assumed to be a permanent sort of thing.

The above examples used sentences that involved indirect reported speech. Though those are the types of examples often used to demonstrate the use of backshifting, backshifting also happens often in other types of construction: constructions where the matrix clause is headed by a past-tense verb form or when the time of the matrix clause situation is the past.

For an example that could use backshifting but that doesn't involving indirect reported speech:

• "Last week, Tom found out that Kim had blue eyes." -- (backshifted)

• "Last week, Tom found out that Kim has blue eyes." -- (not backshifted)

both of the above versions are fine.

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 that the examples I've used are either borrowed from or related to the examples used in the 2005 textbook by Huddleston and Pullum, A Student's Introduction to English Grammar, pages 47-8.

From that textbook, on page 48, is the excerpt:

Although indirect reported speech represents the most obvious case, backshift also happens quite generally in constructions where one clause is embedded within a larger one containing a preterite verb: . . .

.

EDITED:

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.

As a technical matter, he cannot have thought in the past that the Earth is round in the present (because that was in his future); he must have thought that it was round at the time. If you really wanted to refer to his belief then in the Earth's roundness now, the construction would be he thought it would be round, but this is rare in any sensible context. Luckily, the Earth still is round, so you can say either he thinks it is round, he thinks it was round or he thought it was round without offending logic, although the second would draw puzzled glances.

Not one in a hundred English speakers have analysed this, but in my circles the past tense is instinctively used; perhaps because it is in fact correct.