When to use a comma: independent clauses

This is the second in a series of articles about best-practice use of commas. As explained in the previous article, the primary purpose of the comma is to show grammatical independence. There are several ways this might occur. In the previous article, we talked about the importance of separating non-restrictive (another word for independent) phrases from the main clause with commas. When a phrase forms a complete sentence (contains a verb), it’s called a clause. And, like the non-restrictive phrase, we use commas to show that a clause is independent.

Consider the sentence “The owners are responsible for all capital works, and the manager pays for operating expenses.” This is essentially two sentences within a sentence, separated by a comma. In other words, you can remove or change one part of the sentence without changing the meaning of the other part. They are independent clauses. For example, if I changed the subject of the second clause from “manager” to “contractor”, it has no effect on the truth of the first clause.

The rule of grammar that applies in this case is that we separate independent clauses with a comma and connect with a conjunction (that’s the “and” that follows the comma). If you are unsure if a comma is required, simply remove the second clause. If the meaning of the first clause is unchanged, then they are independent clauses and must be separated by a comma.

Whereas, the sentence “The owners are responsible for all capital works while the agreement is in force.” does not take a comma because the second part of the sentence (beginning with the conjunction “while”) makes no sense on its own and restricts the meaning of the first part. Hence, the second part is a dependent clause and must not be separated with a comma. And, just like a restrictive phrase, If you remove a dependent clause from a sentence, the meaning of what’s left behind changes or becomes nonsensical.

We’ll explore more uses of the comma in later articles. You’ll find more plain language explanations of the jargon used in this article in the Doxical Style Guide for Miners and Geoscientists.