grammaticalityrelative-clauses
Can I combine these two sentences:
I'll never forget the time.
We were a happy couple then.
To
I'll never forget the time that we were a happy couple.
And more, without "that"
I'll never forget the time we were a happy couple.
I remember we can use a sentence to describe the objective.
Yes, this can be a possible thought. Everything that @John Lawler has explained is correct. There are a lot of things going on in these phrases.
You have noticed (that) "that" as a relative pronoun may be elided in English without necessarily being ungrammatically correct.
However, "there is to know about you" is not a complete sentence in that it is not an atomic type. Not to be reductive, but it is not an independent clause because it begins with the relative pronoun "that," which would not be diagrammed as an SP.
That "that" is not a conjunction. An easy way to remember the most common coordinating conjunctions is the mnemonic "FANBOYS," for
If it's not on that list, you might be looking at something other than a conjunction.
I hope this helps. What textbook are you using for your studies?
tldr: What’s written is ok, and I’ll show you what it means.
Grammar is something that falls out of the spoken language, not the written one. Punctuation is unrelated to grammar except in that rare circumstance when it signals an audible intonation change meant to alert the listener to some change in the actual underlying grammar. Those cases are hard to come up with, but do exist. All punctuation is just cues for hearing the real language in your head better.
Therefore by that metric, not only is there nothing wrong with the punctuation as written, there cannot be, and no matter how it is written.
So try saying your first example aloud in your head, which I will here write without commas because voices have no commas, just intonation:
This is a restrictive that here, which you can tell because it can be substituted by which with no change in meaning or permissibility:
We can’t use that in descriptive clauses but we can use both that and which in restrictive ones, so if you can swap them, you know what you have. And the other way around, too. This is grammatical whether with or without its comma:
But this is ungrammatical again no matter whether you write the comma or not:
That one is wrong because it tried to use that for a descriptive clause, and you can only use which for those. The native ear goes HUH? when it hears it, which is what makes it ungrammatical.
As you see, it’s never its punctuation which makes something grammatical or ungrammatical. It’s whether you the right worms oops I mean words have managed to put together right — which this sentence almost did not. Twice. :) It had almost managed not to put the right words together, twice.
As you observe, we do not usually use commas before restrictive clauses in English because there is no intonation change to signal there. Presuming that the writer was a competent one, this means the writer was trying to signal something else by including intonation dips. I believe that what he was signalling was an apocopated version of two appositives, which I’ll use em dashes to set off with a repeated things:
If you read his punctuation there, the commas, as an indicator of appositives the same way as they’re used for that in this sentence, his pauses will make much more sense. It’s not especially common, so it’s no wonder it caught your eye, but I believe that there is a legitimate reading where it makes perfect sense.
As for this one:
Here you have to read this for syntactic constituents. The phrase if I’m not mistaken is a parenthetical aside. It could have been written:
So the commas are the same as parens or dashes: they’re there to surround the parenthetical statement. Since in the spoken language you cannot hear any punctuation, this cannot change the grammar. They’re just there to help the reader.
These too are all ok:
All those are fine. About the only thing you can’t do is say:
Because which cannot function there to start the clause to serve as the object of a preposition.
Don’t allow some simple, perhaps simplistic, mnemonic tip for good writing style such as “don’t use a comma before that” confuse you about the larger surrounding issues or about a sentence’s actual grammar. Such tips exist to break a common pattern in beginning writers unfamiliar with the conventions normally observed in these things. But rest assured that the actual grammar remains intact no matter the punctuation, for any grammatical error will jump out to your ear without seeing the punctuation — just like in my very last bulleted example sentence above, the one with the extra asterisk.
Best Answer
I would say, "I will never forget the time when we were a happy couple."