NOTE 1. When singular pronouns, or a noun and pronoun, of different persons, are disjunctively connected, the verb must agree, in person, with that which is placed nearest to it; as, "Thou or I am in fault; I or thou art to blame; I, or thou, or he, is the author of it." But it would be better to say "Either I am to blame or thou art," &c.
2. When a disjunctive occurs between a singular noun or pronoun and a plural one, the verb must agree with the plural noun or pronoun, which should generally be placed next to the verb; as, "Neither poverty nor riches were injurious to him;" "I or they were offended by it."
Constructions like these ought generally to be avoided.
FALSE SYNTAX.
Ignorance or negligence have caused this mistake.
The verb, have caused, in this sentence, is improperly used in the plural, because it expresses the action, not of both, but of either the one or the other of its nominatives; therefore it should be in the singular, has caused; and then it would agree with "ignorance or negligence," agreeably to Rule 9 (Repeat the Rule.)
A circle or a square are the same in idea.
Neither whiteness nor redness are in the porphyry.
Neither of them are remarkable for precision.
Man is not such a machine as a clock or a watch, which move merely as they are moved.