*** I'm not a teacher ***
It's going to be lengthy so grab a coffee! Here's what I've found in
Quirk, Randolph, S. Greenbaum, G. Leech, and J. Svartvik. (1985).A comprehensive grammar of the English language. London: Longman.
1) I wouldn't know about the actual usage but Quirk supports the idea that
neither cannot be used for more choices than two:
In addition to singular and plural number, we may distinguish dual number in the case of both, either, and neither (cj5.16) since they can only be used with reference to two. Both has plural concord (cj6.50); either and neither have singular concord (46.59fl).
2) Further, when it comes to concord he distinguishes between formal and informal situations saying that plural concord is more common in speech:
The rules for the negative correlatives neither. . . nor are the same as for either. . . or in formal usage. In less formal usage, they are treated more like and for concord. Thus, [6] is more natural in speech than [7]:
Neither he nor his wife have arrived. [6]
Neither he nor his wife has arrived. [7]
This preference is probably connected with the use of the plural verb with neither as a determiner or pronoun (cf10.42), but it may also reflect notional concord in that logically 'neither X nor Y' can be interpreted as a union of negatives: 'both (not-X) and (not-Y)'.
3) Since he mentioned that the rules for the negative correlatives
neither . . . nor are the same as for
either . . . or in formal usage, I'll throw in his
either examples to picture the situation with
neither when two nouns don't agree in number. If an asterisk appears after a verb, it means the option's incorrect.
Either the Mayor or her deputy [is/ are*] bound to come. [1]
What I say or what I think [is/ are*] no business of yours. [2]
Either the strikers or the bosses [has*/have] misunderstood the claim. [3]
:arrow:Either your brakes or your eyesight [is/ ?are] at fault. [4]
:arrow:Either your eyesight or your brakes [are/ ?is] at fault. [5]
Grammatical concord is clear when each member of the coordination has the same number: when they are both singular (as in [1] and [2]), the verb is singular; when they are both plural (as in [3]), the verb is plural. A dilemma arises when one member is singular and the other plural (as in [4] and [5]). Notionally, or is disjunctive, so that each member is separately related to the verb rather than the two members being considered one unit, as when the coordinator is additive and. Since the dilemma is not clearly resolvable by the principles of grammatical concord or notional concord, recourse is generally had to the principle of proximity: whichever phrase comes last determines the number of the verb, as in [4] and [5].
So in cases like [4] and [5] where the nouns are of mixed number, we match the verb to the number of the noun in its immediate vicinity.
4) However, he does point out that speakers may still not be comfortable with those structures and so, decide to go for a safer option:
If the number alternatives for the verb are both felt to be awkward, speakers may avoid making a choice by postposing the second noun phrase or sometimes by substituting a modal auxiliary (cf10.44):
Either your brakes are at fault or your eyesight is.
He hasn't arrived, nor has his wife.
Either your brakes or your eyesight may be at fault.