behlmanmeetI'm glad to expand. First, adding a comma between subject and predicate never makes a sentence incomplete. In general terms, if we really do have a proper subject and predicate, then we have all that we need for a sentence. The problem is mainly that we don't
need a comma before the predicate, so its use can cause confusion. Consider a very simple sentence, such as "I like cookies." What happens if we add a comma? "I, like cookies." We still have everything we need for a sentence, but we are left wondering about the purpose of the comma. If we weren't going to add anything, why use a comma? I suppose someone could say this is incomplete in the sense that we expect some kind of intervening modifier and we don't get one, but we don't need a modifier to make a complete sentence. We should simply drop the comma.
So what about a more complex sentence? "The cookies that I baked and that I intended to distribute to my classmates, became too melty in the car." Here, the comma is not strictly needed. We have a subject ("The cookies") followed by directly by a noun modifier with no comma ("that I . . . classmates"), so we can go straight to the predicate without a comma. But is the comma wrong? Not necessarily. In fact, one could argue that it increases clarity by signaling that the long modifier is over and we are returning to the main clause. You and I might not put a comma there, but that doesn't make it 100% wrong. Remember that in real-life writing, we may place a comma anywhere we might take a pause when speaking. The GMAT will be pretty stingy with commas, but it also doesn't tend to test comma usage directly. In other words, an answer with comma problems will usually have other greater problems.
Now, will the GMAT ever actually do this? Specifically, if we attach a modifier to the subject without a comma, will the GMAT add a comma before the verb in a correct answer? Offhand, I can't identify any cases of this, but I'm curious if anyone else can dig one up. Here are a few questions in which the GMAT seems to allow an unneeded comma, but none of them involve a direct break between subject and predicate. However, we can see that the GMAT will sometimes use a comma when joining two noun modifiers or verb phrases, even though we wouldn't typically do that.
https://gmatclub.com/forum/many-policy- ... 49504.htmlhttps://gmatclub.com/forum/at-the-end-o ... 20348.htmlhttps://gmatclub.com/forum/the-rare-bir ... 54228.htmlhttps://gmatclub.com/forum/covering-71- ... 06346.html (This one may seems conventional, depending on how you see the modifiers, but I don't think the "conventional" parallelism interpretation makes much sense.)