Allen and Greenough's New Latin Grammar for Schools and Colleges
J. B. Greenough, G. L. Kittredge, A. A. Howard, Benj. L. D'Ooge, Ed.

1. pater et avus mortuī sunt, his father and grandfather are dead.

[*] Note.--So rarely (by synesis , § 280. a) when to a singular subject is attached an ablative with cum : as,dux cum aliquot “prīncipibus capiuntur” (Liv. 21.60) , the general and several leading men are taken.

[*] a. When subjects are of different persons, the verb is usually in the first person rather than the second, and in the second rather than the third:—

1. “sī tū et Tullia valētis ego et Cicerō valēmus ” (Fam. 14.5) , if you and Tullia are well, Cicero and I are well. [Notice that the first person is also first in order, not last, as by courtesy in English.]

[*] Note.--In case of different genders a participle in a verb-form follows the rule for predicate adjectives (see § 287. 2-4).

[*] b. If the subjects are connected by disjunctives (§ 223. a), or if they are considered as a single whole, the verb is usually singular:—

1. “quem neque fidēs neque iūs iūrandum neque illum misericordia repressit ” (Ter. Ad. 306) , not faith, nor oath, nay, nor mercy, checked him.
2. “senātus populusque Rōmānus intellegit ” (Fam. 5.8) , the Roman senate and people understand. [But, neque Caesar neque ego habitī essēmus (id. 11.20), neither Cæsar nor I should have been considered.]
3. “fāma et vīta innocentis dēfenditur ” (Rosc. Am. 15) , the reputation and life of an innocent man are defended.
est in eō virtūs et probitās et summum officium summaque observantia (Fam. 13.28A. 2), in him are to be found worth, uprightness, the highest sense of duty, and the greatest devotion.

[*] Note.--So almost always when the subjects are abstract nouns.

[*] c. When a verb belongs to two or more subjects separately, it often agrees with one and is understood with the others:—

1. “ intercēdit M. Antōnius Q. Cassius tribūnī plēbis ” (B. C. 1.2) , Mark Antony and Quintus Cassius, tribunes of the people, interpose.
2. “hōc mihi et Peripatēticī et vetus Acadēmia concēdit ” (Acad. 2.113) , this both the Peripatetic philosophers and the Old Academy grant me.

[*] d. A collective noun commonly takes a verb in the singular; but the plural is often found with collective nouns when individuals are thought of (§ 280. a):—

1. (1) “senātus haec intellegit” (Cat. 1.2) , the senate is aware of this.
2. “ad hīberna exercitus redit ” (Liv. 21.22) , the army returns to winter-quarters.
plēbēs ā patribus sēcessit (Sall. Cat. 33), the plebs seceded from the patricians.
3. (2) “ pars praedās agēbant” (Iug. 32) , a part brought in booty.
4. “cum tanta multitūdō lapidēs conicerent ” (B. G. 2.6) , when such a crowd were throwing stones.

[*] Note 1.--The point of view may change in the course of a sentence: as,equitātum omnem ... quem habēbat praemittit, “quī videant” (B. G. 1.15) , he sent ahead all the cavalry he had, to see (who should see).

[*] Note 2.--The singular of a noun regularly denoting an individual is sometimes used collectively to denote a group: as, Poenus, the Carthaginians; mīles, the soldiery; eques, the cavalry.

[*] e. Quisque, each, and ūnus quisque, every single one, have very often a plural verb, but may be considered as in partitive apposition with a plural subject implied (cf. § 282. a):—

1. “sibi quisque habeant quod suum est ” (Pl. Curc. 180) , let every one keep his own (let them keep every man his own).

[*] Note.--So also uterque, each (of two), and the reciprocal phrases alius ... alium alter ... alterum (§ 315. a).