When I used to hire copy editors for large academic projects, I got to know the work of each talented editor quite well. I learned a lot from reviewing the changes and choices they made. As the years went by, I also became familiar with what one editor would focus in on as opposed to what another might focus in on. This awareness allowed me to assign work to people who were the best fit for whatever a manuscript needed. Now a full-time copy editor myself, I realize how easy (perhaps comforting) it is to get into this kind of copyediting groove/rut/nitpickiness, whatever you want to call it. Although you copyedit a work for all rules of grammar and style, your eye trains itself, with a little help from your compulsive brain, to look for certain things to “correct.” And sometimes those little things you always correct, much for your own sense of accomplishment, are things that no one really cares about. Here are some things I often find to correct but suspect that if I didn’t, few might notice, and because I do, some might wonder why.
comprise vs. compose: I look this one up a lot to refresh my memory and placate my OCD because it comes up often. The best way for me to explain the rule to authors, and myself, is that comprise means “includes,” whereas compose means “makes up.” You’ll find explanations that the whole comprises the parts, and the parts compose the whole. It gets tricky when a sentence says something such as “Adolescents comprise 20% of the US population,” which seems like two equals, but I tend to skirt the issue and just replace with “make up” (a fellow editor also suggests “constitute”) because compose feels awkward in these cases.
each other vs. one another: Each other is for two, and one another is for more than two. He and I love each other, but we all love one another. Few authors may love this being changed for what might seem like no reason.
not only … but also: More than a pet peeve, this one is essential. It is vital that we not only correct this construction in every piece of writing but also feel confident about why we are doing so. Whatever follows not only must parallel that which follows but also. A quick tip is to remove the words between and including not only and but also, and the sentence should still make sense. That is, “It is vital that we feel confident about why we are doing so.” You might often see statements like “It is not only vital that we correct this construction in every piece of writing but also feel confident about why we are doing so.” In such a case, we’d have to say “but also vital that we feel confident about why we are doing so.” That is too many words to say the same thing, so the previous version is much better. Watch out for commas! There should only be a comma before but also if the subsequent text has both a subject and verb, which it rarely does (for the reason just given; also see commas below).
since vs. because: Since has to do with time but can also mean because. When used for other than its temporal definition, I would often edit for because, but I have since let go of this insistence because it is too strict. See what I did there? Note that because often should not have a preceding comma (see commas below).
where vs. in/at which: I will often change where to in which when not referring to a physical location. That is, “We are in a political environment where beliefs are touted over facts” will become “We are in a political environment in which beliefs are touted over facts.”
which vs. that: In American English, which has been reserved for nonrestrictive clauses, whereas that is for restrictive ones. Webster’s gives a history of usage and concludes that which can now be used for both nonrestrictive and restrictive clauses. British English does allow which in restrictive clauses. But depending on the work, I still make the distinction between the two, and if the clause is essential to the sentence, I will edit for that. Which clauses are then within commas (see commas below).
while vs. whereas or although: I used to focus on this one too much, changing uses of while to restrict it to just its temporal meaning and using whereas and although when those were more precise. But some authors seem to prefer while for just about everything, so now I edit for this occasionally to limit the number of whiles in a paragraph. Note that while when used to mean “at the same time” does not require a comma; when it is used as whereas or although, there is a comma (see commas below). I do still often edit for whereas when I can. It’s my little way of trying to keep that word in circulation. You’re welcome.
commas: All copyediting roads eventually lead to commas. Sometimes I feel like half of what I do is mess around with commas. Take one out here, but then place it over there. Remove them from compound predicates. Add them when two independent clauses are joined by a conjunction. And authors come from different backgrounds with different ideas of how to use the comma, which is fine. There is some leeway. Many people still believe the comma should be used for every pause one might take in a sentence. More than one author has disagreed with imposing a strict comma policy on their work. One author even went so far as to fax me pages from his 1960s college writing manual to prove that he, not I, was correct. So, do your best with commas, and then let the author have their way if they disagree. That seems to work best. But commas do make a big difference in how one reads and understands a sentence, so the important work must go on.