It's been a while since I've done one of these, so let's celebrate the unofficial beginning of fall with a GrammarScribe Grammar Tip!
Sometimes commas are used inappropriately in text when two clauses are linked with “and” or “but.” A comma can be inserted mistakenly because a pause would occur while speaking, but the use of commas in writing differs somewhat.
An easy rule of thumb: Insert a comma if a new subject is introduced in the second clause, or if the initial subject is restated. Otherwise, leave it out so the second half of the sentence isn’t divorced from the first half.
Incorrect: Jack went into the storeroom to look for supplies, but couldn’t find anything. (The second part of the sentence should have its own subject or the comma should be removed.)
Correct: Jack went into the storeroom to look for supplies but couldn’t find anything.
Correct: Jack went into the storeroom to look for supplies, but he couldn’t find anything.
Correct: Jack went into the storeroom to look for supplies, but Locke found them first. (New subject; so a comma is required.*)
*Like just about every rule in this crazy language of ours, there's an exception. It's okay to omit the comma between short coordinate clauses. Example: She went to the store but he stayed home.
I'd like to make GrammarScribe Grammar Tips a regular feature on my blog. Do you have any burning grammatical questions that need an explanation? What are some common errors that you'd like to see addressed? Leave a comment and let me know!