Ablative of Accompaniment
When Caesar marches cum tribus legiōnibus — "with three legions" — that cum + ablative names the company he keeps along the way. Accompaniment is the social ablative: who or what is travelling, fighting, or living alongside the subject.
"with X" — names the company kept by the subject.
Bare ablative for accompaniment is the exception, restricted to military nouns with an adjective. When in doubt, use cum.
See It In Action
— A&G §413 (Cic.)
Textbook accompaniment. cum + ablative names the company the subject moves with — this is the form to default to whenever a person or group goes along with the action.
— B. G. ii. 19
Caesar keeps cum here even though the noun is military. The bare-ablative exception (§413.a) needs an adjective in tow — omnibus cōpiīs, magnīs cōpiīs. With plain nouns Caesar still reaches for cum.
Both can show up as a noun in the ablative — the form doesn't tell you which.
person or group travelling alongside; takes cum + abl. (military phrases drop cum with an adjective)
cum amīcīs vēnit
"he came with his friends"
concrete instrument used to perform the action; bare ablative, no preposition
gladiō interfectus est
"he was killed with a sword"
Tip: Two questions disambiguate: (1) Is the noun a person? If yes, default to accompaniment with cum. (2) Is there a preposition? If cum is present and the noun is something the subject travels or fights with, it's accompaniment.
In Caesar omnibus cōpiīs prōficīscitur — there's no cum. Why is the bare ablative correct here?
Study Tips
- •Default rule: accompaniment uses cum + ablative. If you see a person or group ablative without cum, look hard at context — it's probably means or manner instead.
- •The big exception is military phrases: Caesar drops cum freely with cōpiīs, legiōnibus, exercitū when an adjective is in tow — omnibus cōpiīs, magnīs cōpiīs, tribus legiōnibus. Bare ablative reads as accompaniment when the noun is a fighting force.
- •Words of contention — pūgnāre, certāre, contendere, dīmicāre, bellum gerere — always take cum + abl. for the opponent. Cum hostibus pūgnāre, never bare hostibus.
- •Accompaniment vs. means: a person with cum is accompaniment ("with my friends"); a thing without cum is usually means ("with a sword").