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.

[*] a. Adjectives of fitness or use take oftener the Accusative with ad to denote the purpose or end; but regularly the Dative of persons:—

1. aptus ad rem mīlitārem, fit for a soldier's duty.
2. “locus ad īnsidiās aptior ” (Mil. 53) , a place fitter for lying in wait.
nōbīs ūtile est ad hanc rem (cf. Ter. And. 287), it is of use to us for this thing.

[*] b. Adjectives and nouns of inclination and the like may take the Accusative with in or ergā :—

1. “cōmis in uxōrem ” (Hor. Ep. 2.2.133) , kind to his wife.
2. “dīvīna bonitās ergā hominēs ” (N. D. 2.60) , the divine goodness towards men.
3. “dē benevolentiā quam quisque habeat ergā nōs ” (Off. 1.47) , in regard to each man's good will which he has towards us.
4. “grātiōrem mē esse in tē ” (Fam. 11.10) , that I am more grateful to you.

[*] c. Some adjectives of likeness, nearness, belonging, and a few others, ordinarily requiring the Dative, often take the Possessive Genitive:—¹

1. “quod ut illī proprium ac perpetuum sit ... optāre dēbētis ” (Manil. 48) , which you ought to pray may be secure (his own) and lasting to him. [Dative.]
2. fuit hōc quondam proprium populī Rōmānī (id. 32), this was once the peculiar characteristic of the Roman people. [Genitive.]
cum utrīque sīs maximē necessārius (Att. 9.7A), since you are especially bound to both. [Dative.]
3. “prōcūrātor aequē utrīusque necessārius ” (Quinct. 86) , an agent alike closely connected with both. [Genitive.]

The genitive is especially used with these adjectives when they are used wholly or approximately as nouns:—
1. amīcus Cicerōnī, friendly to Cicero. But, Cicerōnisamīcus, a friend of Cicero; and even, Cicerōnisamīcissimus, a very great friend of Cicero.
2. “crēticus etêius aequālis paean ” (Or. 215) , the cretic and its equivalent the pœan.
3. “hī erant affīnēs istīus” (Verr. 2.36) , these were this man's fellows.
After similis, like, the genitive is more common in early writers. Cicero regularly uses the genitive of persons, and either the genitive or the dative of things. With personal pronouns the genitive is regular ( meī , tuī , etc.), and also in vērī similis, probable:—
1. “dominī similis es ” (Ter. Eun. 496) , you're like your master (your master's like).
2. “ut essēmus similēs deōrum” (N. D. 1.91) , that we might be like the gods.
3. “est similismâiōrum suom ” (Ter. Ad. 411) , he's like his ancestors.
4. “patris similis esse ” (Off. 1.121) , to be like his father.
sīmia quam similis turpissima bēstia nōbīs (N. D. 1.97, quoted from Enn.), how like us is that wretched beast the ape!
5. sī enim hōcillī simile sit, est illud huic (id. 1.90), for if this is like that, that is like this.

[*] Note.--The genitive in this construction is not objective like those in § 349, but possessive (cf. § 343).