Using commas with “and” and “but”

Using commas with and and but

About a month ago, I wrote a post about a common comma mistake: separating the subject and the verb with a comma. Here, I’m going to tackle how to use commas with the coordinating conjunctions and and butOf course, we use commas with these coordinating conjunctions in lists, but I’m not here to discuss the serial comma today. I want to talk about using commas with and and but to separate independent clauses.

Coordinating conjunctions

Let’s quickly talk about coordinating conjunctions. Coordinating conjunctions are handy little words that we use to join parts of a sentence. There are seven coordinating conjunctions: for, and, nor, but, or, yet, and so. A good way to remember them is with the acronym FANBOYS.

The words nor, for, yet, so, and to some extent or are less common than and and but, and they also have their own little quirks; and and but are the most common of the bunch and follow straightforward rules, so I’m going to focus on them. They also seem to trip up writers the most often when it comes to comma usage.

Like I said at the beginning of this post, we use a serial comma before and when we list items in a series (e.g., A, B, and C). Most writers know this, so I want to focus on independent clauses.

Use a comma before and and but when joining two independent clauses

Outside of the context of the serial comma, a comma should only precede and and but if one of those words joins two independent clauses. As I’ve discussed before, an independent clause can stand alone as its own sentence; it has a subject and a verb and expresses a complete thought. Here’s an example:

My dog ate garbage last night, and he was sick in the morning.

This example contains two independent clauses (“My dog ate garbage last night” and “He was sick in the morning”) joined with the coordinating conjunction and. Using a comma before and in this context signals to the reader that what follows is a complete thought and an independent clause.

Only omit this comma if the two independent clauses are short and closely related:

Mom called and I answered.

However, be aware that omitting the comma can sometimes confuse your reader. Consider the following example:

My sister likes vegetables and cake makes her sick.

There are two independent clauses in this sentence: “My sister likes vegetables” and “Cake makes her sick.” Because vegetables and cake are both foods, though, a reader might initially misread the sentences as “My sister likes vegetables and cake.” When in doubt, use a comma in this context; it is never wrong.

Avoid using a comma if what follows the and or but is not an independent clause. Here’s an example of a misused comma with and: 

My dog ate garbage last night, and was sick this morning.

There is one independent clause in this example because there is only one subject: dog. Adding a comma before and here separates the subject from one of its two verbs and therefore breaks the rule I discussed in my last comma post.

This is English, so of course there’s an exception. If you have more than two verbs attached to a single subject, then treat those verbs as you would any other series:

Lucy bought a coffee, had a sip, but dropped her cup on the sidewalk. 

A good way to think about this issue is to treat the verbs as list items. I would never write “I like cats, and dogs”; I would simply write “I like cats and dogs.” Think of verbs the same way: “I like cats but hate dogs,” not “I like cats, but hate dogs.” I would, however, write “I like cats, love dogs, but adore bunnies.”

Conclusion

Use a comma before and or but if joining two independent clauses. If you only have one independent clause but more than one verb, treat the verbs like any other list or series. That is, use a serial comma to set off the final verb in the series from and or but. 

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