Is "so that" considered as one whole conjunction or separate words entirely?
For instance, if I had the sentence "The boy crossed the road so that he could get to the other side.", would "so that" be a conjunction or just a part of one main clause entirely?
Any help would be appreciated~ 
Yes, “so that” as a whole is a conjunction by itself. It is a
subordinating conjunction meant to show the purpose of an action or to give an explanation for that action.
Let’s examine the use of “so that” in your sentence in particular: “The boy crossed the road
so that he could get to the other side.” The action described in the main or independent clause, “The boy crossed the road,” is expected to bring about the expected result described in the subordinate clause, “
so that he could get to the other side.” The subordinator “so that” establishes the logical relationship between the causing action and the resulting action.
This particular logical relationship, however, can also be established even if “so” acts as a conjunction without the word “that.” Take a look at this sentence: “The boy crossed the road
so he could get to the other side.” Here, in the absence of “that,” we have two coordinate clauses of equal grammatical rank—meaning that none of the two is subordinate to the other: the first is “the boy crossed the road,” and the second, “he could get to the other side.” What we have here are two independent clauses linked by “so,” this time working as a
coordinating conjunction. In this sentence construction, the first clause is the action and the second clause is the response to that action, and their logical relationship is established by “so” as a coordinating element.
Formally, when “so” is used as a coordinating conjunction, a comma is required to set off the second clause from the first clause, as in this sentence: “The partners settled their differences
, so their joint project can proceed.” That comma is intended to indicate that “so” is being used as coordinating conjunction for the two independent clauses. In informal writing, however, that comma is often dropped without making the sentence grammatically or structurally wrong: “The partners settled their differences
so their joint project can proceed.”
Take note, though, that when “that” is dropped in a sentence where “so that” is actually meant as a subordinating conjunction (as is the case with the revised version of your sentence), putting a comma between the main clause and the subordinate clause can destroy the sense of the sentence (at least in writing). The sentence becomes disjointed when we put that comma: “The boy crossed the road
, so he could get to the other side.” Take out that comma and the logic of the sentence gets restored: “The boy crossed the road so he could get to the other side.” The moral here, of course, is that when dropping “that” from “so that” constructions in writing, it is important to play it by ear whether to keep that comma or not.
As to your last question on whether “so that” in your sentence would be a conjunction or just a part of the main clause, let me make this clarification: When “so that” is used as a subordinating conjunction as is the case with your sentence, it becomes an integral part of the subordinate clause; indeed, it becomes what’s called a
subordinating marker—identifying and relegating the clause that follows it to a subordinate status: “…
so that he could get to the other side.” On the other hand, when “so” links two independent and coordinate clauses, as in “The partners settled their differences
, so their joint project can proceed,” it’s neither a part of the independent clause nor of the subordinate clause. It is there only as a link—a coordinating element—between two independent clauses of equal grammatical rank.
