One of the things I have noticed over the years is that today’s writers have an aversion to using commas. Think about it: how often have you been reading a book when, all of a sudden, you lose track of the meaning of a sentence and have to re-read it? It happens to me all the time. Yes, it could be that my ADHD is partially to blame, but, more often than not, it’s usually because there wasn’t a comma where one ought to have been.
Here’s an example of what I’m talking about: The plane landed with a bump and Jerry heard the roar of the engines when they were slammed into reverse. The sentence ought to read: The plane landed with a bump, and Jerry heard the roar of the engines when they were slammed into reverse. The rule that governs this is: Use a comma before any coordinating conjunction (and, but, for, or, nor, so, yet) that links two independent clauses.
The same rule applies in this next sentence: A women in her late twenties sat alone within the waiting room and in her left hand she held a keychain of pink rabbit fur. The sentence should read: A women in her late twenties sat alone within the waiting room, and, in her left hand, she held a keychain of pink rabbit fur. The comma after the word and is used to separate the two independent clauses. However, the comma after the word, hand, is governed by another rule: Use commas to offset appositives from the rest of the sentence. In this example, in her left hand is an appositive, a phrase that offers additional information about the second independent clause, she held a keychain of pink rabbit fur.
Another comma that has been eliminated (incorrectly, I might add) is the serial comma, also known as the Oxford comma. This is the last comma in a series. Example: They spotted two prostitutes, an Asian man, and an Italian woman. There are four individuals alluded to in the sentence. However, when the final comma is eliminated, the meaning of the sentence becomes quite different. They spotted two prostitutes, an Asian man and an Italian woman. In this sentence, there are only two individuals—an Asian man and an Italian woman—and both are prostitutes. The rule goes like this: Use commas to separate items in a series.
In my opinion, these examples are the ones that lead to the most confusion. For a complete list of “comma rules,” see A Guide to Proper Comma Use – Business Insider.