In English parts of a sentence must agree in form with each other as well as with certain other words— objects and complements. A complete sentence should contain two parts: a subject and a predicate. The subject is ‘what’ or ‘whom’ the sentence is about, while the predicate tells something about the subject. The predicate (a verb) may be followed by a direct object or an indirect object that completes the predicate’s meaning. To determine if a verb is followed by a direct object, isolate the verb and make it into a question by placing ‘whom? or ‘what?’ after it. An indirect object, as a rule, is a noun or pronoun and in a sense the recipient of the direct object. To determine if a verb has an indirect object, isolate the verb and ask ‘to whom?’, ‘to what?’, ‘for whom?’, or ‘for what?’
The sentence ‘Jenifer’s fiancé, so highly acclaimed by her, has never given her a bouquet of flowers’ contains both a direct object ‘a bouquet of flowers’ and an indirect object ‘her’.
English learners know that the predicate, i.e. the verb form may be affected by whether its subject is in the first person (I), the second person (you), or the third person (he, she, it) and by whether the subject is singular or plural, and native speakers pick up this part of grammar as they learn to talk.
Applying the principles of agreement is not very difficult, nevertheless, errors do occur when the predicate has two subjects, e.g. should it be ‘either you or I is crazy’, or ‘am crazy’, or ‘are crazy’? Here the verb has two subjects but it should agree with only one, which one?
In ‘either . . . or’ the accepted convention is that the noun nearer to the predicate determines the form of the verb, i.e. ‘either you or I am reckless, and either I or you are reckless’.
Similarly it should be ‘neither you nor I am reckless, note that ‘neither of us is reckless’ is correct.
However, when the second subject is preceded by ‘not’, the verb agrees in person with the first subject, e.g. ‘You, not I, are reckless, but ‘It is you that is reckless’ here the verb in the relative clause beginning with ‘that’ should agree with.
When the subjects are joined by ‘or’ as in the example, ‘The taxi driver or the porter was probably involved in the crime’ the predicate should agree with each subject individually.
When one of the subjects is singular and the other is plural, the number of the verb is determined by the number of the closer subject: ‘The taxi driver or the porters were involved in the crime’.
Likewise with ‘neither… nor’ the same rule should be followed, i.e. ‘Neither the porters nor the taxi driver was involved in the crime’ or ‘Neither the taxi driver nor the porters were involved in the crime’.
Like the rule for determining the person of the verb in such cases. Note that paired subjects of different number are far more likely to occur than paired subjects of different person, as in the example ‘A guest or two was standing at the entrance’, such sentences do not follow the accepted convention and both forms of a verb – singular ‘was’ and plural ‘were’ are correct.
Subjects Preceded by ‘Not’
In the examples ‘I think the porters, not the taxi driver, were involved’, or ‘I think the taxi driver, not the porters, was involved. The subject preceding ‘not’ determines the form of the verb, whether or not it is closer to the verb. The second subject can be repositioned, i.e. ‘I think the porters were involved, not the taxi driver’.
Subjects joined by ‘But’, ‘Not only… But also’
‘I think not the porters but the taxi driver was involved’, ‘I think not only the taxi driver but also the porters were involved’. Here if the verb occurs with the subject preceded by ‘not only’, it agrees with that subject: ’I think not only were the porters involved but also the taxi driver’ and ‘I think not only was the taxi driver involved but also the porters’.