When to use a comma: more about phrases and clauses
Let’s do a quick recap. The primary function of the comma is to show grammatical independence. This can occur in several ways, such as to:
Separate items in a series
Separate independent adjectives
The comma is also used to create certain grammatical constructions, including:
Introductory phrases
Conditional clauses
Transitional words or phrases
So far, we’ve covered non-restrictive phrases and independent clauses. In this article, we’ll talk about the role of commas when forming introductory phrases, transitional phrases, and conditional clauses. Don’t worry about the jargon: I’ll explain it as we go.
Introductory phrase
Consider the sentence “The operator must move the switch to the off position before engaging the engine.” This sentence ends with a prepositional phrase (the bit starting “before…”). If we move the prepositional phrase to the start of the sentence, it’s called an introductory phrase: “Before engaging the engine, the operator must move the switch to the off position.” And because we are moving away from standard word order, we add a comma to tell the reader where the introductory phrase ends.
This is often done in instructional writing to preface an instruction with a warning or condition (also see conditional clauses below). More generally, prepositional phrases help to establish the context of the sentence for the reader. It’s just good writing practice. Here’s another example: “In the summer, temperatures can exceed 40 degrees.” Introductory phrases can also start with a participle (verb ending with -ing or -ed), as in “Assuming the worst case, we have closed the plant.” So whenever you see a sentence start with a preposition (before, in, after, with, to, during, under, until, despite, etc.) or a participle (assuming, referring, concerning, considering, notwithstanding, owing to, provided, regarding, respecting, etc.), you’ll know there’s a comma coming.
Transitional word or phrase
A transitional word or phrase creates a logical connection between phrases, clauses, or sentences. This might indicate a contrast, consequence, addition, reinforcement, or an example. Commonly used transitional words and phrases include however, hence, also, similarly, consequently, meanwhile, nevertheless, moreover, furthermore, after all, even so, in addition, in other words, that is, as such, for example, and as a result. For example, this sentence begins with a transitional phrase. Similarly, this one begins with a transitional word. A transitional word or phrase, however, can appear anywhere in the sentence, like this. And when they do, we separate them from the rest of the sentence with commas. You get the idea.
Conditional clause
A conditional clause states a hypothesis or condition. Typically, a conditional clause starts with “if”, and the consequential clause starts with “then”. If you see an if…then construction, then separate the two clauses with a comma, like this. However, be aware that the “then” is sometimes omitted, but the comma is still required. The conjunctions unless, provided that, and as long as are also commonly used to start a conditional clause. The if…then construction is called a correlative conjunction, which come in pairs. Other correlative conjunctions, such as not only…but also, either…or, neither…nor, and both…and, also take a comma.
We’ll explore the remaining uses of the comma in the final article of this series. You’ll find plain language explanations of the jargon in the Doxical Style Guide for Miners and Geoscientists.
