Is using "that" twice in a row "that that" poor grammar?

I think that would depend on whether “I must go so that she may stay” or similar is ungrammatical. I suspect not.

It’s possible my use of “so” isn’t actually replacing one of the "that"s in that sentence. I may just be adding a word and then eliding a “that.” Still, “gave their lives so that” sounds more normal to my ears.

Yes, that example is suppressing a “that.” “So that” is a phrase, and “that nation” is demonstrative of what nation. That example seems more problematic to me. If you read “so that” together, then nation stands alone without an article, which is odd. Reading the “that” as belonging to nation seems to put undue emphasis on which nation.

I don’t see the problem with that. “That nation” is in the original, so Lincoln was himself putting emphasis on which nation. Otherwise he would have said “the nation” (or even “a nation,” to make it more general).

I also note that, when you have have two "that"s together, you usually (if not always) deemphasize one of them and emphasize the other. I suspect that Lincoln most likely read that statement as “…gave their lives th’t that nation may live…,” which still puts emphasis on the second “that.”

Yes, I mentioned the emphasis on my earlier post. That’s why I said undue emphasis. It reads differently to me with only one that. It sounds less like it is referring back to a nation already referenced, and more like, that nation as opposed to all other nations. Your mileage may vary.

We did this when I was in third grade, circa 1960. We had a poem to read, of which I only remember the ending. It was about a Christmas stocking, stuffed so full that a debate arose as to whether anything more could be put into it. A mouse came and chewed a little hole in the stocking, and then concluded:
    I think you’ll agree
    That that little hole
    Was not in there before!

Mrs. Dalton pointed out to us 3rd-graders that the word “that” was there twice, which we might not have noticed, and that it was perfectly correct, and that we should put a bit more emphasis on the second “that”.

Same here. Even though English speakers tend to omit “that”, there are other languages that require “that”. So for translation purposes, it is much better to make sure that all “thats” are are included.

It’s not poor grammar, but if you have a problem with it, then it’s poor writing. If the most obvious and concise phrasing sounds clunky or weird, you’re not obliged to use it.

@eschrodinger put things very well, but there is one other thing I’d like to bring up. Imagine that you’re addressing a group of people, many of which have done some deed worthy of praise. And many people in the group have been the recipients of some such action. If you’re not going to use names (and there are various reasons why you might not want to), then you need some other way of specifying a particular person. In the context of a speech, you’re probably not going to use any physical descriptors, such as what the person is wearing. Thus, the best way of distinguishing people is to use other descriptors, such as “that person” vs. “this person.”

In addition, “that” can be used as an intensifier–putting the audience on notice that you are meaning one particular thing out of a group of things. Thus, you NEED two instances of that; the first one is in the phrase “so that,” and the second one is in the phrase “that person/nation/whatever.”

I think that in the construction “so that that” being shortened to “so that”, it’s not the second “that” that’s being omitted; it’s the first. In English, “so” can be used in place of “so that”, as can be seen in a sentence with only one (or zero) “that”.

“I gave my dog food so that he could eat”
“I gave my dog food so he could eat”.

Yes, it’s common in everyday speech to suppress “thats.”

There was a documentary about the making of the popular TV show How It’s Made, called How How It’s Made is Made.

When it was released on DVD, there was also a small bonus featurette on the making of the documentary called How How How It’s Made is Made is Made

(none of the above is true, however, if I had to create a title for this post, it might be How How How How it’s Made is Made is Made was Made)

Here’s something similar I remember from high school. It was given to me unpunctuated, and the class was supposed to put in commas and double quotes.

John, where Mary had had “had,” had had “had had.” “Had had” had had the Teacher’s approval.

In its original, unpunctuated state, it was unbelievable:

John where Mary had had had had had had had had had had had the Teacher’s approval.

Damn. Beat me to it.

John, where I had had “had” had “had had”. “Had had” had had the teacher’s approval.

Ninjad. Damn.

“That” is both a relative pronoun and a demonstrative. The relative usage is generally unstressed (and can often be omitted, although not always). The demonstrative usage is generally stressed. This isn’t the only example of part of speech being determined by patterns of stress. The following illustrative sentence is also literally true: “The brown BUILDING on the McGill campus is the BROWN building.” Actually the William M. Brown building and whoever specified a brown brick facade must have done it consciously.

There is also the do-do phenomenon:

You may not believe it, but I do do everything by the book.

mmm

I, too, have a bathroom vanity drawer full of reading material.

The shame.

The repeated use of “had” arises, in part, from there being two distinct meanings: It is a helper verb commonly used to create the past perfect of a verb; but it is also the plain-old past tense of “to have”. Nothing prevents these two uses from happening together, to produce all those “had had” sentences.

Fuller version:

that that is is that that is not is not that that is is not that that is not that that is not is not that that is is that not it it is

There are at least a couple of verses in the KJV of the Bible with “for for”.
Example: Romans 6:13. For for this cause pay ye tribute…
NIV has it as: This is also why you pay taxes.

It’s a matter of taste perhaps, but I prefer:

John, where Mary had had “had,” had had “had had;” “had had” had had the Teacher’s approval.

It’s just as valid but now the repetitions occur in the middle of one sentence rather than at ends of two different ones.