Punctuation: Commas, Semicolons, Colons, Apostrophes and Quotes

Mastering Commas in Sentences and Series

A compound sentence contains at least two independent clauses joined by a coordinating conjunction (usually with a comma) or by punctuation such as a semicolon or colon. The coordinating conjunctions can be remembered easily by the acronym FANBOYS: for, and, nor, but, or, yet, and so. A comma is normally placed before a coordinating conjunction joining two independent clauses, although it may be omitted when the clauses are short and closely related. However, a comma should not be used before a coordinating conjunction if the sentence contains a compound predicate sharing one subject.

Joining two independent clauses incorrectly results in serious structural errors. Joining two independent clauses with only a comma produces a grammatical error known as a comma splice. Conversely, joining two independent clauses without any punctuation or conjunction creates a fused or run-on sentence. A comma splice can be corrected by adding a coordinating conjunction, changing the comma to a semicolon, or using a period.

Clauses also require careful comma placement depending on their position and role. An introductory dependent clause is normally followed by a comma; a comma may be omitted after a short clause when the meaning remains clear. In contrast, a dependent clause that follows an independent clause usually does not require a separating comma. Commas are also used to set off parenthetical expressions and transitional phrases such as 'for example' or 'in fact.'

Within sentences, commas are used to separate three or more individual items or phrases in a series. The Oxford comma is the comma placed immediately before the coordinating conjunction in a list of three or more items. Additionally, nonrestrictive or nonessential clauses must be set off from the rest of the sentence with commas, whereas restrictive or essential clauses provide necessary identifying information and do not take commas.