This is the grammatical term for the distinction between the singular and the plural.
Unsurprisingly, a singular noun takes a singular verb (takes being an example of that), while plural nouns take plural verbs (that was another example, in case you missed it).
Where there are two subjects in the sentence, the verb is generally plural (Diligence and enthusiasm are desirable in an articling student).
It’s easy to lose the plot, however, when the two components of a compound subject are separated by a lot of intervening material.
A case in point is a clause a lawyer recently asked me about. Which wording is correct?
- The division of this Agreement into articles and sections and the use of headings is for convenience of reference only and does not modify or affect the interpretation or construction of this Agreement or any of its provisions.
- The division of this Agreement into articles and sections and the use of headings are for convenience of reference only and do not modify or affect the interpretation or construction of this Agreement or any of its provisions.
It has to be version 2, because the subject of the sentence is The division … and the use – so the verbs should be are and do.
This is the general rule, but there are times when the two elements of a compound subject are inextricable, and therefore demand a singular verb: Scotch and soda is her favourite drink; gin and tonic is mine. Or where they could be said to constitute a single concept: Violence and killing is against moral law (the subject of the sentence being, in effect, violent killing: Fowler’s example from Modern English Usage).
On that rationale, the boilerplate provision about consideration could be the receipt and sufficiency of which is hereby acknowledged — but one also sees are hereby acknowledged.
Don’t stretch things too far with compound subjects, though.
And where it’s X or Y rather than X and Y, the verb will accord with the nearest element (in this case, Y): Either the company or its directing minds are liable BUT Either the directing minds or the company is liable.
Another common pitfall is the one in [larger number] formulation, which often ends up in error. It isn’t One in ten doctors smoke but One in ten doctors smokes. (The subject of that sentence is One (singular) not doctors (plural).)
Next: the subjunctive