I just watched this video at pros write on verb-subject agreement. Worth watching if you think you have trouble with agreement. It nicely explains that native speaker of English don’t normally have any trouble with agreement rules when the subject is immediately next to the verb. Problems only crop up when the subject has a modifier that ends with a noun. An example given in the video is:
Accurate estimates for delivery has stopped
The error is that “has” should be “have”. The video simplifies things a little at this point and identifies the subject as estimates, which is why the verb should be plural “have” instead of singular “has”. This is a perfectly acceptable simplification too – the actual story is more than business writers need to know about.
But we’re all grammar lovers here, so let’s dig a little deeper. Here’s the simplified syntax tree:
NP stands for “noun phrase”, VP stands for “verb phrase”, PP is “prepositional phrase” and AdjP you can probably guess is “adjective phrase”. Aux is an auxiliary verb.
When you look at the sentence structurally like this, you can see that delivery is not really “next to” the verb at all. It’s tucked away inside a much larger noun phrase, and it isn’t in the right position to act as subject all by itself. When we plan sentences in our heads, we’re not planning linear strings of words, we’re planning something more hierarchical, like that tree, and I bet this agreement problem crops up less in speech (although that’s an empirical question I suppose).
Anyway, the point I want to get to is that the subject is not a word like estimates but a position in the sentence. In particular, it’s the noun phrase daughter of the sentence. So the true subject here is the entire noun phrase accurate estimates for delivery.
It has always struck me as odd how much attention agreement gets in prescriptive grammars. Why is this such a big deal? There’s almost no agreement to speak of in our language. First, agreement is limited to verb-subject agreement. Second it’s limited to the present tense. Third, with the exception of to be, verbs have only two present tense forms: -s for “third person” vs. no suffix for “everything else”. Look at an Athabaskan language for goodness’ sake. The fact that English speakers need a ten minute video on have/has starts to look a little absurd.