What is the function of "this" in the following sentence:
My father made this farm what it is
Is it a determiner? When do I use it as a complementizer?
This is a determiner and used to indicate close proximity or ownership. For example, if I'm standing next to a dog and want to indicate that it's mine, I would say, "This is my dog." If my dog has wandered a few yards away and a stranger picks her up (perhaps intending dognapping), I would say, "That is my dog."
1 a (1) : the person, thing, or idea that is present or near in place, time, or thought or that has just been mentioned these are my hands (2) : what is stated in the following phrase, clause, or discourse I can only say this: it wasn't here yesterday b : this time or place expected to return before this 2 a : the one nearer or more immediately under observation or discussion this is iron and that is tin b : the one more recently referred to
"This" can't be a complementizer, but that is another role for "that."
From Richard Nordquist: https://www.thoughtco.com/what-is-complementizer-1689770
In English grammar, a complementizer is a word used to introduce a complement clause, including subordinate conjunctions, relative pronouns, and relative adverbs. For example, if functions as a complementizer in the sentence "I wonder if she will come."
In some contexts the complementizer that can be omitted — a process known as "that complementizer deletion." For example, "I wish that I had duck feet" can also be expressed as "I wish I had duck feet." The result is called a null complementizer.
In generative grammar, complementizer is sometimes abbreviated as Comp, COMP, or C. The words "that," "if" and "to" are the most popularly utilized complementizers in the English language, though the list of complementizers is quite a bit more extensive.
Although not exhaustive, Laurel J. Brinton lays out a list of the most commonly used complementizers in the English language book "The Structure of Modern English: A Linguistic Introduction." This list includes while, since, because, although, if, when, so that, as such, before, after, until, as long as, as soon as, by the time that, once, and inasmuch as."
That, if, and to have special usage as complementizers. For that, the compliment associated with a complement type is named the that-clause and may or may not be omitted and still make sense in the context of a sentence. If can function in the exact same manner as "that" as in "I don't know if John will join us."
As Michael Noonan describes in "Complementation," the word to is used in conjunction with most infinitives wherein "neither the verbal noun nor participial complement types have complementizers in English."