§411. Uses of the Ablative As Instrumental

Opus and ūsus, signifying need, take the Ablative:—¹

• magistrātibus opus est (Leg. 3.5), there is need of magistrates.
• nunc vīribus ūsus (Aen. 8.441), now there is need of strength.

a. With opus the ablative of a perfect participle is often found, either agreeing with a noun or used as a neuter abstract noun:—

• opus est tuā exprōmptā malitiā atque astūtiā; (Ter. And. 723), I must have your best cunning and cleverness set to work.
• properātō opus erat (cf. Mil. 49), there was need of haste.

b. Opus is often found in the predicate, with the thing needed in the nominative as subject:—

• dux nōbīs et auctor opus est (Fam. 2.6.4), we need a chief and responsible adviser (a chief, etc., is necessary for us).
• sī quid ipsī opus esset (B. G. 1.34), if he himself wanted anything (if anything should be necessary for him).
• quae opus sunt (Cato R. R. 14.3), things which are required.

Ablative of Manner