Research for this book shows that five of the most common errors in college writing involve commas. Check your writing for these errors:
Check every sentence that doesn’t begin with the subject to see whether it opens with an introductory element (a word, phrase, or clause that tells when, where, how, or why the main action of the sentence occurs). Use a comma to separate the introductory material from the main part of the sentence. (54b)
Look at every sentence that contains one of the conjunctions and, but, for, nor, or, so, or yet. If the groups of words before and after the conjunction both function as complete sentences, you have a compound sentence. Use a comma before the conjunction. (54c)
Look at each adjective clause beginning with which, who, whom, whose, when, or where, and at each phrase and appositive. Decide whether the element is essential to the meaning of the sentence. If the rest of the sentence would be unclear without it, you should not set off the element with commas. (54d)
Identify all adjective clauses beginning with that, and make sure they are not set off with commas. (54d and 54k)
Do not use commas to set off restrictive elements; between subjects and verbs, verbs and objects or complements, or prepositions and objects; to separate parts of compound constructions other than compound sentences; or before the first or after the last item in a series. (54k)