Welcome back to my crash course in basic Grammar. Today’s blog is centered around the comma in a compound sentence.
First, let’s define what a compound sentence is.
According the Chicago Manual of Style, (the end-all authority,) a compound sentence joins clauses by using a coordinating conjunction. (Coordinating conjunctions include words such as and, but, or, so, and yet.)
The rule is:
IF you have two independent clauses joined with the coordinating conjunction, there IS a comma.
The easiest way I know how to explain an independent clause is that it can stand alone – it expresses a complete thought. (It is really a stand-alone sentence, but it is joined with another complete thought in one sentence.)
For instance: The Uber didn’t get there, so we took a taxi.
‘The Uber didn’t get there,’ is a complete sentence, and so is, ‘We took a taxi.’ They are joined by the coordinating conjunction, so.
Because the two joined clauses are both independent, you use a comma before the conjunction. Think of it as though neither of these clauses needs the other. Therefore, the comma separates them.
Conversely, IF you have an independent clause joined with a dependent clause, there is NOT a comma.
A dependent clause does NOT express a complete thought on its own. It needs the other part of the sentence – the independent clause to make it a complete sentence.
Because the two joined clauses NEED one another to express the thought, there is NOT a comma. (I think of it as a form of codependency.)
For instance: We will sign the proposal if you accept all of our demands.
‘We will sign the proposal,’ is an independent clause – it expresses a complete thought.
‘You accept all of our demands,’ is NOT a complete thought, therefore it DEPENDS on the first part of the sentence. They are joined by the coordinating junction, OR, and no comma is appropriate in this instance.
I use this rule on a daily basis. You do too. Some of us learned this a long time ago in high school English, while some of us still struggle with it. In my editing process, I read each sentence one at a time. I evaluate any sentences where there is a coordinating conjunction – and, but, or, so, and yet, and I look at both of the clauses.
Are they both independent? (Could they both stand alone?)
IF yes, then there IS a comma before the ‘and,’ ‘but,’ etc.
Is one of the clauses dependent? (Does it need the other part of the sentence to make sense?)
IF yes, then there IS NOT a comma before the coordinating conjunction.