Of all the punctuation marks, I believe the one used and thereby misused the most is the common comma. Some poets choose to ignore it or simply to ignore all punctuation, and that seems to be acceptable, particularly with the free verse crowd; however, I am inclined to think punctuation (along with proper capitalization) makes one’s writing very clear and if it is ignored at all, it should be done at the hands of someone very skilled in his/her writing and who can make line breaks which clearly show his/her meaning.
So what are the rules of commas? I will begin with the obvious ones most people learn in grade school and the ones many people seem to already know instinctually.
Rule 1: Commas are placed to set off items in a series (items which, by the way, are parallel in structure), for example, a series of nouns, a series of verbs, etc. A comma is not needed after the last item named in a series: She ate an apple, a sandwich, potato chips and a doughnut.
Rule 2: Commas set off place names and dates: He has lived at 818 Mulberry Lane, in Cedar Rapids, Iowa, since Jan. 3, 1964. (Notice the address number isn’t separated from the street name by a comma)
Rule 3: A comma is placed after a direct address or greeting: Mom, where are you?
Rule 4: Commas separate quotations from the sentences in which they are found:
“I am going to Indiana,” she said, “to see my uncle.” However, when a sentence quoted is a completed one, a period is placed before the continuing sentence:
“I am going to Indiana,” she said. “I will see my uncle there.”
Rule 5: A comma precedes an afterthought or contrast as in these two example: The concert was great, better than I thought. It was romantic, not comedic.
Rule 6: Commas separate a series of adjectives before a noun; however, a comma should not come between the final adjective and the noun: He is a smart, happy boy.
Rule 7: A comma comes after an introductory word or phrase. Examples of common introductory words and phrases are these: of course, on the other hand, in fact, yes, no, well, nevertheless, however, in my opinion, that is to say, therefore, then, also, etc. Furthermore, if these words and phrases interrupt a sentence, the comma would be around them: I am going, by the way, to New Orleans.
Finally I will address the area I think causes the most confusion with comma placement. This type of comma usage, most likely to occur in a poem , involves compound sentences or sentences containing adverb or adjective clauses. First, a comma is placed before coordinating conjunctions and, most importantly, when those coordinating conjunctions (connecting words) are connecting two independent clauses. What this means is that on both sides of the connecting word there must be a complete sentence with a subject and a verb. First, there is an acronym often used for the seven connecting words. It is FANBOYS (FOR/AND/NOR/BUT/OR/YET/SO). Notice in my first example, I will not use a comma in front of the coordinating conjunction: “She lives in New York and flies to London.” In this example, “flies to London” is not a complete independent clause. There is no subject, only the verb “flies.” In my next example, the sentence will be changed so that by adding in the word “she” into the second clause, I have a true compound sentence with two independent clauses: “She lives in New York, and she flies to London.” Of course, modern English now does not even require such a short compound sentence to have a comma. To be on the safe side, however, it’s good to use the comma in a true compound sentence.
If two clauses are not connected using one of the words represented by FANBOY, one can be fairly certain the sentence is one with a dependent and independent clause. These types of complex sentences are joined with words such as these: before, after, while, as, since, if, unless, although, even though, because, provided that, etc. These adverb clause “markers” are at the front of the dependent clause of a complex sentence as in “After he ate dinner, he rested.” In this sentence, the meaning of “after he ate dinner” is not complete until we see the second part, the independent clause “he rested.” When a dependent clause comes at the beginning of the sentence, it IS followed by a comma. Now here is where it gets tricky! If the dependent clause comes AFTER the independent clause, a comma is not placed in the sentence at all, as in “He rested after he ate dinner.” I think many people get confused with the word “because,” wanting to put a comma in front of it, but it is not done. One must write “We ate dinner quickly because we were so hungry,” NOT “We ate dinner quickly, because we were so hungry.” It is a myth that a comma always replaces a pause. There can be a pause within a sentence employing an adverb clause, but that doesn’t mean we must put a comma in front of the adverb clause marker.
Finally, I want to discuss adjective clauses and phrases. These can be restrictive or non-restrictive. Simply put, restrictive means it’s necessary to the meaning of the sentence. Non-restrictive, or non-essential, means it’s just extra information. In a sentence like “The girl whom he likes is very friendly,” one cannot know anything about the girl unless I say “whom he likes.” Therefore, it’s a restrictive adjective clause and commas should NOT be used. If I said, on the other hand, “Angela, whom he likes, lives in LA,” I have identified the girl as Angela, so the fact he likes her is extra information and needs to have commas around it. This rule also works for adjective phrases, which are the reductions of adjectives clauses (clauses beginning with who, whom, which, that, etc.) A phrase, unlike a clause, does not have a subject. Here is an example of a non-restrictive “appositive” phrase: I am excited to see Paris, the most beautiful city in the world.
Reductions of adjective clauses also use -ed or -ing participles, such as in this sentence using a restrictive phrase: “The people living in that neighborhood are disgusting.” Once I name or identify those people, I will have a NON-restrictive phrase and I will not use a comma as in this example: “The Smiths, drinking and laughing all night, were disgusting.” The phrase “drinking and laughing” is considered extra information, whereas in the previous example, “living in the neighborhood” was vital to the meaning of who the people were, and so commas were NOT used around that first example’s phrase.
That’s it for my explanation of comma rules. Study the rules. They are all over the internet. Using punctuation correctly reflects good writing!