As the backbone of effective communication, punctuation is an essential component of the writing process. To ensure successful comprehension for both the writer and the reader, proper punctuation is needed to write clearly and accurately. One key to proper punctuation is knowing how to use a comma correctly in a complex sentence.

In general, a comma is typically used to separate two independent clauses, or sentences. An independent clause contains a subject and predicate, and is able to stand alone as a sentence as well. Before using a comma to separate two independent clauses, one should make sure that the clauses are joined by one of the coordinating conjunctions: for, and, nor, but, or, yet, or so. If two clauses are joined by a conjunctive adverb—words like however, moreover, therefore, and thus—a comma is usually needed before and after the conjunctive adverb.

When a conjunction is used to connect two related sentences, a comma is usually used before the conjunction. This is true of both compound sentences and complex sentences. In a compound sentence, two independent clauses are joined by a coordinating conjunction. For example, “She swept the floor, and she washed the windows.” In a complex sentence, an independent clause is combined with a dependent clause. A dependent clause is a part of a sentence that cannot stand alone as a sentence but that provides additional information. For example, “She swept the floor, because it was dirty.”

The comma is also used to set off introductory elements, mid-sentence interrupters, and parenthetical information, or information and phrases that are not essential to a sentence’s meaning. For example, “He drove to the store, reluctantly, in his truck.” A comma is also sometimes used to separate items in a list. For example, “She bought milk, eggs, and bread at the store.”

When using a comma in a sentence, it is important to be aware of this versatile punctuation mark’s potential to either add clarity or create confusion. Proper use of a comma can help emphasize the individual elements of a complex sentence while still allowing the reader to distinguish them clearly. Following the above rules should make proper punctuation of complex sentences—including the use of a comma—a breeze.