That:

Описание: In this video, I begin the process of answering two questions:

(1) Is there REALLY such a thing as a NON-RESTRICTIVE Appositive--AND a RESTRICTIVE Appositive?
(2) Is there REALLY such a thing as a NON-RESTRICTIVE Noun Complement--AND a RESTRICTIVE Noun Complement?

In my NEXT video, #13c, I'll give my answers to the above questions, and I'll thoroughly explain why I answered them as such.

ADDENDUM (26 December 2023)
Let's look at THREE examples of how the clause “that he was advancing” can be used in a sentence.

Example #1: The proposition that he was advancing was preposterous. “that he was advancing”: the STRUCTURE is that of a Distinction/Relative Clause. However, people get confused when they see this structure because its physical structure is exactly the SAME as a Noun Clause. In this particular application of the clause, the word “that” is a Distinction Indicator (poorly referred to as a Relative Pronoun). The Distinction Indicator lets you know that you are dealing with a Distinction Phrase/Clause—that is, a phrase/clause that will make a DISTINCTION about the word “proposition.” As such, its FUNCTION could be said to be simply that of a Distinction Clause, or, when considered in an extended form, a Noun Complement. Intention: The speaker of the sentence is trying to get you to FOCUS on ONE particular thing—and one only: “the PROPOSITION that he was advancing”—the THING that he was advancing. Summary: “that he was advancing” is a Distinction/Relative Clause functioning as a Noun Complement.

Example #2: The proposition that he was advancing was preposterous.
“that he was advancing”: the STRUCTURE is that of a Noun Clause; its FUNCTION is that of a Noun Complement.
Intention: the speaker is trying to impart the following: Even though there COULD very well be other propositions, he is specifically addressing ONE single proposition (the one that “he” was advancing). Unlike with the above Distinction Clause, which focused on the “thing” itself, this clause is used in this fashion to let you know that even if there are indeed OTHER propositions, the speaker is referring categorically to only ONE of those propositions—only ONE thing.
Summary: “that he was advancing” is a Noun Clause functioning as a Noun Complement.

Example #3: The proposition, that he was advancing, was preposterous.
“that he was advancing”: the STRUCTURE is that of a Noun Clause; its FUNCTION is that of an Appositive. (The commas help identify it as such.)
Intention: the speaker is trying to impart the following: Someone, say a supervisor or manager, was suggesting that an employee (the “he” in the Noun Clause) will be “advancing,” or “getting promoted.” The remaining employees think that the promotion is unwarranted and ridiculous—that is, preposterous. The FOCUS is on “renaming,” or “emphasizing,” the word “proposition.” In this application of the clause “that he was advancing,” we are being told that there is ONLY one proposition in question; there are NO other propositions.
Summary: “that he was advancing” is a Noun Clause functioning as an Appositive.

When you ponder the different examples, you will, at some point, see that the featured clause—“that he was advancing”—acting as a Distinction Clause is providing DIFFERENT information from that which it provides as a Noun Complement or Appostive.
Employing a Distinction Clause, the sentence is trying to tell you “what's happening to the proposition.” A PROPOSITION is being advanced.
Employing a Noun Complement or an Appositive, the sentence is trying to tell you “what's happening to the person being addressed.” That is, the PERSON is being advanced.

If you think the above through logically, you will understand what I've just presented. And you must remember that a single sentence is rarely “isolated”; that is, the sentence must be considered in the CONTEXT of the discourse. You must first determine whether the clause is a Distinction Clause or a Noun Clause. If it's a Noun Clause, you must next determine WHAT exactly that Noun Clause is doing in the given sentence. Consider “structure” and “function.” From there, you get “meaning.”