Conjunctions Part 2: To Comma or Not to Comma

In my last grammar tip, I discussed starting sentences with coordinating conjunctions. Today I want to answer the second of the two common conjunction questions:

• Is it correct to start a sentence with and, but, or yet in formal writing even though my writing and grammar-check software says I shouldn’t?

• When I start a sentence with a coordinating conjunction, should I follow it with a comma as my writing software often says I should?

A common error I see writers make concerns coordinating conjunctions (like but, so, and yet) that begin sentences. Microsoft Word often causes writers to multiply these errors because its grammar-check tool suggests commas both where they are optional and where they don’t belong.

Most online resources I’ve looked at explain either coordinating conjunctions or conjunctive adverbs but not both in the same place. I tend to remember rules better if I understand what’s happening beneath the covers. In this case, the answer involves both parts of speech. So I’ve laid out an answer for you below that explains comma use for both.

Coordinating Conjunctions versus Conjunctive Adverbs
To answer the comma question, we must understand the difference between a coordinating conjunction (for, and, nor, but, or, yet, so) and a conjunctive adverb.

• Coordinating conjunctions connect grammatically similar parts (independent clause to independent clause, word to word, phrase to phrase). They must occur in a sentence or paragraph in a position between the two items connected.

• Conjunctive adverbs are modifiers that provide transition as well as logical connection and can occur in positions other than directly between the two logically connected ideas.

 
✓ Conjunctive adverbs may occur in several places; therefore, I can write a sentence with them between two independent clauses as long as I use a semicolon.
 
✓ Conjunctive adverbs may occur in several places; I can place them in a sentence, therefore, at either the beginning, middle, or end.
 
✓ Coordinating conjunctions must occur between the connected parts, so I cannot place them at the middle or end.
 
✘ Coordinating conjunctions must occur between the connected parts; I cannot write them, so, in the middle or end.
 
A coordinating conjunction makes no sense thrown to the middle of the independent clause.
 

• If a coordinating conjunction needs a comma, as it does between two independent clauses, that comma will go before the conjunction: We went to the movies, and they went to dinner.

• If a conjunctive adverb needs a comma, that comma might go after the adverb as in the first example above or before and after the adverb as in the second example.

• A conjunctive adverb cannot connect two independent clauses with a comma. In the first example above, the semicolon is the syntactical joiner for the two clauses while the conjunctive adverb therefore modifies write and adds a logical rather than syntactical connection to the first clause.

Which One Takes the Introductory Comma?
Let’s move now to discussing the two parts of speech at the beginning of simple sentences rather than in the middle of compound or complex sentences.
 

• When a coordinating conjunction begins a sentence as I showed they could in Part 1, it needs no comma after it.

✘ Yet, people often put them there incorrectly.
✓ Yet people often put them there incorrectly.

• When a conjunctive adverb begins a sentence, a comma usually follows it, according to the rules of introductory modifiers. The basic rule, which has exceptions, is that a comma should follow an introductory modifier.

✓ Thus, this conjunctive adverb has a comma following it.

Why Does My Grammar Checker Get This Rule Wrong?
The coordinating conjunctions yet and so also function as several other parts of speech, including adverbs. What you see in your grammar-check apps (MS Word, Grammarly, and others) when they tell you to “add a comma after the introductory modifier” is a default labeling problem.

Because these programs prefer avoiding coordinating conjunctions at the start of a sentence, the artificial intelligence (AI) labels these multifunction words at the beginning of sentences— erroneously—as conjunctive adverbs. 

Now you know more than your AI and how to respond.
 
Morals to This Story
1. Know your list of seven coordinating conjunctions.
2. Keep using that grammar-check software, but also use your grammar brain.

Inklings at Work (and Play)

Pick a page or two of your recent work and scan for conjunctions and commas. How are you doing? Are you getting this rule right?

Is the comma after “but” in the second sentence below correct or incorrect? Why?
 

When you sit down to write, first take time to brainstorm past surface ideas. But, as you prepare, remember that your true purpose is to write!