Dative with Adjectives
A small closed list of Latin adjectives reaches outward — they can't stand alone, they need someone or something to be friendly to, fit for, near to, like to. That target sits in the dative.
Tribūnī nōbīs sunt amīcī — "the tribunes are friendly to us." Castrīs idōneus locus — "a place suitable for a camp."
Four families cover almost every case you'll meet: similarity (similis, dissimilis, pār, impār), friendliness (amīcus, inimīcus, fīdus), fitness (aptus, ūtilis, idōneus), and nearness (propinquus, vīcīnus, fīnitimus).
The trap is similis, which also takes the genitive — patris similis, "like his father." With persons especially, Cicero prefers the genitive; with things, either case works.
"X (similar / friendly / fit / near) to/for Y" — the dative names what the quality reaches toward.
Closed list — four families: similarity, friendliness, fitness, nearness. Similis also takes the genitive, especially with persons.
See It In Action
— B. G. ii. 17
idōneus ("fit") reaches outward to castrīs — the dative names what the place is fit FOR. Caesar uses this construction whenever scouts are looking for ground.
— B. G. v. 44
inimīcus illī — the dative names whom Vorenus is enemy TO. The whole point of Caesar's anecdote turns on this: Pullo and Vorenus are personal rivals, and the dative carries that tie.
— Verg. Aen. vi. 522
simillima morti — similis with the dative of the THING resembled. With persons Cicero would lean genitive (patris similis), but Vergil's morti is a thing, and the dative reads cleanly.
Similis alone among these adjectives takes BOTH cases. The choice tracks what's being compared and how closely tied the two are.
general resemblance; thing-to-thing
simillima morti
most like a (peaceful) death
intrinsic likeness; person-to-person, esp. with pronouns
patris similis
(just) like his father
Tip: Ask: am I comparing to a PERSON (especially with personal pronouns meī, tuī)? Lean genitive. A THING or abstract quality? Dative reads more naturally. Vērī similis ("probable") is always genitive.
In castrīs idōneum locum dēlēgit ("he chose a place suitable for a camp"), what is castrīs doing?
Study Tips
- •Memorize the four families (similarity, friendliness, fitness, nearness) — almost every dative-with-adjective you meet on the AP exam belongs to one of these twelve words.
- •When you see similis, check whether the noun beside it is dative or genitive — both are correct, but Cicero leans genitive for persons (patris similis) and dative for things.
- •Watch for aptus and ūtilis taking ad + accusative instead of dative when the goal is a thing or purpose (aptus ad rem mīlitārem) — the dative survives for persons.