Commas

Q. Is it correct or incorrect to put a comma before the “and” in the following sentence: “The Department of Justice has taken on the role of coordinating agencies’ activities, and has undertaken several new initiatives related to dealing with criminals.” I think it’s correct because the second clause—although not an independent clause, strictly speaking—is so long (and the subject is implied). The comma seems to help the reader get through the sentence. Many thanks.

A. The comma isn’t necessary, but if you want to indicate a pause, add it anyway. Please see CMOS 6.16: “The comma, aside from its technical uses in mathematical, bibliographical, and other contexts, indicates the smallest break in sentence structure. Especially in spoken contexts, it usually denotes a slight pause. Effective use of the comma involves good judgment, with ease of reading the end in view.”