Do not use commas to set off restrictive elements that are necessary to the meaning of the words they modify. Do not use a comma before a coordinating conjunction (and, but, for, nor, or, so, yet) when the conjunction does not join parts of a compound sentence (error 13). Do not use a comma before the first or after the last item in a series, between a subject and verb, between a verb and its object or complement, or between a preposition and its object. (See 19i.)