One of the most common mistakes writers make is to insert commas where they are not needed. Because the comma is so helpful and its uses so varied, many writers sprinkle them liberally throughout their text – even when they do not quite belong. But however unassuming they seem, a misplaced comma can lead to embarrassing shifts in the meaning of a sentence – sometimes comical but other times disastrous.
While there are always exceptions to every rule, the following pointers provide a general guideline for when NOT to use a comma in your writing (all incorrect examples of sentences are in italics)
• No commas to connect verbs: There is no need to use a comma to separate the verb from the rest of the sentence. In the following example, the comma is incorrect: “The author carefully reviewed, the long manuscript.” Take out that comma after “reviewed” and keep your verbs connected.
• No comma between independent clauses: When you have two clauses that could stand alone (independent clauses) and you wish to show a close relationship between them, link them with other punctuation or with a conjunction, depending on the meaning you are going for. Avoid linking them with a comma, as shown incorrectly here: “There was a knock at the door, the author stopped writing.” This is known as a comma splice and should only be used in very rare cases between very short, equally weighted clauses: “I came, I saw, I conquered.” The following text shows just some solutions for repairing the comma splice in the previous example. Each option changes the meaning subtly.
o Add a semi-colon: “There was a knock at the door; the author stopped writing.”
o Add a coordinating conjunction: “There was a knock at the door, and the author stopped writing.”
o Add a subordinating conjunction: “There was a knock at the door, so the author stopped writing.”
o Add a long dash: “There was a knock at the door—the author stopped writing.”
• No comma between two actions performed by one subject: When two actions are made by the same subject, the general rule is that they should not be separated by comma. For example, “The author opened the door, and looked outside,” is incorrect. Exceptions to this rule are when there are three or more actions, because in this case the actions form a list (and therefore take commas). For example, “The author opened the door, looked outside, and found the parcel.”
• No comma between two subjects performing the same action: Just as two actions by the same subject should not be separated, two subjects (a compound subject) simultaneously taking the same action should not be separated either. For example, “The author, and his editor worked all through the night” is incorrect. But again, when there are three or more subjects this forms a list of items which should be separated by commas: “The author, his wife, and his editor worked all through the night.”
• No commas to separate restrictive clauses: It is a good idea to learn how to recognize restrictive clauses versus non-restrictive clauses in a sentence. These clauses both give a little more information about the subject of the sentence, but non-restrictive clauses, which often start with “which” as this clause did, are parenthetical (non-essential) information and should be surrounded by commas. “The puppy, which was sleeping on the pile of papers, had chewed the manuscript to pieces.” In this sentence, the information about where the puppy is sleeping is not essential to understanding the sentence and could be removed (non-essential) without affecting the main clause.
On the other hand, a restrictive clause takes no commas because it is essential to the rest of the sentence (this type of information is often introduced with a “that”). For example, this is incorrect: “The puppy, that was sleeping on the pile of papers, had chewed the manuscript to pieces.” Remove both commas, because while this is a similar sentence it implies there might be other puppies in the room and we are only talking about that puppy: the one on the papers. When you add information to describe one particular subject (among possible others), it should not be separated by commas.
These are some good general rules to keep in mind when writing. Remember, knowing the rules (and when they can be broken) adds to your writer’s “toolkit.” By learning the basic grammar and punctuation rules, you can add layers and subtleties to your writing that would not have been possible otherwise – an important step on the journey to becoming a professional writer.