Passive Periphrastic (Obligation)
When a gerundive (the -ndus, -nda, -ndum form) sits next to a form of esse, Latin stops describing ordinary passive and starts asserting obligation. Carthāgō dēlenda est, Cato's drumbeat, doesn't say 'Carthage is being destroyed' — it says 'Carthage MUST be destroyed.'
Two details do all the work. The tense lives in esse (est / erat / erit / sit). The agent — the person on the hook — stands in the dative, never in ā/ab + ablative the way every other passive marks its agent.
Mihi faciendum est = 'I must do it.' If the verb is intransitive, the gerundive goes neuter impersonal: eundum est, 'one must go.'
Learnings0 core · 1 AP claim
AP framework claims (1)— verbatim from AP CED
'X must / has to / will have to be done by Y' — tense from esse, agent in DATIVE.
Agent is mihi / tibi / nōbīs (dative), NEVER ā mē / ā tē / ā nōbīs. Intransitive verbs go neuter impersonal: eundum est = 'one must go.'
See It In Action
— Cic. Cat. 1. 11
Textbook personal periphrastic: gerundive habenda agrees with the subject gratia (fem. sg.), and est fixes the tense as present. 'Must be given' — the necessity, not the action, is what Cicero is asserting.
— B. C. iii. 85. 4
Caesar in indirect speech. One nōbīs governs two gerundives (differendum, cogitandum) — Latin shares a single dative-of-agent across coordinated periphrastics.
— Cic. Cat. 4. 18
Impersonal periphrastic with de + ablative. Vōbīs is dative agent ('by you'), not indirect object — and English most naturally inverts it to active 'you must judge.'
— B. G. ii. 5. 2
Impersonal periphrastic of an intransitive verb (confligō + cum). No subject, no agent expressed — just the abstract necessity. Tense lives in sit (present subjunctive in a ne-clause).
'X must be V-ed by Y' — preserves the dative agent as English 'by'
Carthāgō nōbīs dēlenda est = 'Carthage must be destroyed by us'
'Y must V X' — flip dative into subject, periphrastic into modal
mihi faciendum est = 'I must do it' / 'I have to do it'
'one must V' / 'we must V' — active reading is the only readable one
eundum est = 'one must go'; nōbīs cogitandum = 'we must think'
'had to be V-ed' / 'will have to be V-ed' — tense lives in esse
faciendum esset = 'had to be done'; agitanda erit = 'will have to be raised'
Two ways Latin marks the doer of a passive verb. The trigger is purely grammatical: gerundive + esse forces dative; every other passive takes ā/ab + ablative.
person on whom the obligation rests
Carthāgō nōbīs dēlenda est
Carthage must be destroyed by us
person who actually did the action
Carthāgō ā Rōmānīs dēlēta est
Carthage was destroyed by the Romans
Tip: Look at the verb form FIRST. -ndus/-nda/-ndum + est/erat/erit/sit → the agent will be a bare dative. Any other passive (perfect -tus est, present -tur) → expect ā/ab + ablative.
In Caesar's differendum est… nōbīs et de proeliō cogitandum (B. C. iii. 85. 4), what does the construction differendum est express, and what is nōbīs?
Study Tips
- •Spot the construction in two beats: see -ndus/-nda/-ndum, then look for a form of esse (est, erat, erit, sit, esse). If both are there, translate 'must / has to / had to / will have to.'
- •When you meet a bare dative next to a passive periphrastic — mihi, tibi, nōbīs, vōbīs — that dative is the AGENT, not an indirect object. No ā/ab is coming.
- •If the verb takes the dative or is intransitive (serviō, pāreō, eō, cōgitō dē), expect the impersonal neuter: temporī serviendum est, eundum est. Translate active in English: 'one must…' / 'we must…'