Conjunctions on the ACT

Yes, I’m sure all of you know what a conjunction is. We’ve all heard the famous song on “School House Rock.” (If you haven’t, please youtube it; you’re missing out on some pretty essential pop culture.)  My goal is not to tell you the difference between “and,” “but,” and “or.” My goal is to explain how conjunctions are used to link phrases and clauses.
The ACT will likely test you on two kinds of conjunctions: coordinating conjunctions and subordinating conjunctions. Each type has its own set of rules that you must follow.

Coordinating Conjunctions– For, And, Nor, But, Or, Yet, So

Coordinating conjunctions are those conjunctions that connect words, phrases, and, most importantly, independent clauses. To remember the coordinating conjunctions, use the mnemonic device FANBOYS: For, And, Nor, But, Or, Yet, So. We already know that coordinating conjunctions can be used to link words (I need to buy milk and cookies) and phrases (John needs to run home and do his homework).
The most important function of the coordinating conjunction, however, is its ability to connect two independent clauses with a comma. An independent clause is a complete idea (containing a subject and verb) that can stand alone as a complete sentence. Let’s see some examples of the coordinating conjunction in action:
 

Wrong: I decided to skip work, therefore I’ll be able to watch the game.  ”Therefore” is not a coordinating conjunction!
Notice that the comma and the conjunction separate independent clauses. “I want to watch the game” and “I have to work that day” can stand as complete sentences, so they are independent clauses. The important rule to know is that, if one side of the conjunction is not an independent clause, I don’t need a comma:

Notice that I changed this sentence so that “I can go to work,” an independent clause, is now “go to work,” a simple phrase. As a result, I removed the comma since the conjunction no longer divides two independent clauses.

Subordinating Conjunctions– Because, Before, After, When, Since, Until, Although, While

Like coordinating conjunctions, subordinating conjunctions help to connect two independent clauses, but they can only do so by making one of the clauses dependent (i.e. subordinate). When I place a subordinating conjunction in front of an independent clause, I render that clause dependent, thereby facilitating its linkage with an independent clause.
Comma use with subordinating conjunctions depends on the placement of the clauses:

1. When the independent clause comes first, you don’t need a comma.
2. When the dependent clause comes first, you need a comma to separate the clauses.

Here are some examples of this difference:

Notice that each sentence has two clauses, one of them independent and the other dependent. The clause “because I forgot to study” is dependent; it cannot stand alone as a sentence. If we were to remove “because,” though, “I forgot to study” would function as an independent clause. The subordinating conjunction renders the clause dependent.
A common error is placing a comma before the subordinating conjunction in the second form:

In this example, you simply do not need a comma when you place the dependent clause after the independent clause. As you can see, conjunctions are accompanied by specific comma rules. As you all know, the ACT loves to test for comma usage, so beware of comma placement when you see conjunctions like these.