There are two: per + accusative and operā + genitive.
- Recall that operā (sans ā/ab) is operating as an Ablative of Instrument
- These are constructions where the agent/instrument sense breaks down: with per, animate agents seems to work as instruments, and with operā, the (instrumental) labor of an agent take the place of that agent.
Agents with Per Construction
- Caesar was informed by scouts: Caesar ab explōrātōribus certiorātus est.
- Cesar was informed by scouts: Caesar per explōrātōrēs certiorātus est.
- He was trampled by charioteers: ab origīs compressus est.
- He was trampled by charioteers: per origās compressus est.
Agents with Operā Construction
- Caesar was informed by scouts: Caesar ab explōrātōribus certiorātus est.
- Caesar was informed by the work of scouts: Caesar operā explōrātōrum certiorātus est.
- The walls were cleaned by a slave: mūrī ab famulō lōtī sunt.
- The walls were cleaned by slave’s labor: mūrī operā famulī lōtī sunt.
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While we’re at it, note the odd forth principle part of wash: lāvō, lāvāre, lāvī, lōtum.
- Really, it varies: it can also be lautum or lāvātum, depending on the author.
The Essential AG: 405b
Latin for Addicts 