An active–passive transformation preserves the event but changes its grammatical viewpoint. The active direct object becomes the passive subject, and the active subject may be retained as an agent. Latin then rebuilds the verb so that it agrees with the new subject. This is a structural transformation, not the insertion of one word meaning English “be.”
The passive is most straightforward with a transitive verb that takes an accusative object. It is useful when the affected participant is already the topic, when the agent is unknown or unimportant, or in impersonal (formal) reporting. Classical prose does not prefer passive voice in every context; choose it because the information flow calls for it.
The larger morphological contrast is surveyed in Active and Passive Voice; this page concentrates on how to produce and revise the transformation.
Map the roles before changing any forms
Begin with a plain active clause:
Mīlitēs pontem mūniunt.
The soldiers fortify the bridge.
Its structure is subject mīlitēs + direct object pontem + active verb mūniunt. For the passive:
- promote accusative pontem to nominative pōns;
- change active mūniunt to passive mūnītur;
- if the old subject remains, express it as personal agent ā mīlitibus.
Pōns ā mīlitibus mūnītur.
The bridge is fortified by the soldiers.
The singular new subject controls singular mūnītur. The old plural subject no longer controls the verb. If the soldiers are obvious or irrelevant, omit the agent: Pōns mūnītur.
Form the passive in the present system
Present, imperfect, and future passives are synthetic: passive endings are attached to the tense stem. The subject's person and number still control the finite verb.
| Active | Passive | Value |
|---|---|---|
| laudat | laudātur | praises → is praised |
| laudābat | laudābātur | was praising → was being praised |
| laudābit | laudābitur | will praise → will be praised |
| regunt | reguntur | rule → are ruled |
| capiunt | capiuntur | capture → are captured |
Magister discipulōs laudābat.
The teacher was praising the students.
Discipulī ā magistrō laudābantur.
The students were being praised by the teacher.
Accusative plural discipulōs becomes nominative plural discipulī, so imperfect passive laudābantur is plural. The tense and ongoing viewpoint remain imperfect.
Form the passive in the perfect system
The perfect, pluperfect, and future perfect passives use a perfect passive participle plus a form of sum. The participle agrees with the passive subject in gender, number, and case; sum agrees in person and number.
| Active | Passive | Value |
|---|---|---|
| mūtāvit | mūtātus/-a/-um est | changed → was/has been changed |
| mūtāverat | mūtātus/-a/-um erat | had changed → had been changed |
| mūtāverit | mūtātus/-a/-um erit | will have changed → will have been changed |
Senātus lēgem mūtāvit.
The senate changed the law.
Lēx ā senātū mūtāta est.
The law was changed by the senate.
Feminine nominative singular lēx requires mūtāta, not default masculine mūtātus. For a neuter plural subject, both participle and auxiliary are plural: Cōnsilia mūtāta sunt “the plans were changed.”
English “was changed” can describe an event or a resulting state. Latin perfect passive mūtāta est ordinarily belongs to the verbal perfect system. Context distinguishes a true event from an adjectival participle plus sum.
Personal agent versus means or instrument
A person or personified agent is normally expressed by ā/ab + ablative. Use ab before a vowel and commonly before h; ā is usual before most consonants.
Porta ā custōde aperta est.
The gate was opened by the guard.
An instrument or means normally takes the bare ablative, without ā/ab:
Porta clāvī aperta est.
The gate was opened with a key.
The distinction is semantic. The guard intentionally performs the action; the key is the means used. Natural forces often take a bare ablative of cause or means, though authors may personify them and use ā/ab. Do not copy every English “by” with ab.
Preserve other complements
Only the direct accusative object is normally promoted. An indirect object remains dative, and adverbial expressions retain their functions.
Cōnsul mīlitibus praemia dedit.
The consul gave rewards to the soldiers.
Praemia mīlitibus ā cōnsule data sunt.
Rewards were given to the soldiers by the consul.
The accusative praemia becomes nominative, but recipient mīlitibus remains dative. Time, place, manner, and dependent genitives likewise stay attached to the event or their head nouns. A transformation should not indiscriminately change every case.
Not every active clause has an ordinary personal passive
An intransitive verb has no direct object to promote. Latin can use an impersonal passive in the third-person singular with some intransitive verbs:
Mīlitēs fortiter pugnāvērunt.
The soldiers fought bravely.
Ā mīlitibus fortiter pugnātum est.
There was brave fighting by the soldiers.
The neuter singular participle pugnātum belongs to an impersonal construction; it does not mean that some hidden object “was fought.” Such passives are common in narrative or (formal) prose but require separate practice.
Deponent verbs have passive-looking forms with active meaning, such as hortātur “he encourages” and secūtus est “he followed.” They cannot be mechanically converted into a passive by retaining the same forms. Use another verb or recast the sentence. Likewise, verbs governing a dative or ablative rather than an accusative may form impersonal passives, not a promoted personal subject.
Worked prompt 1: present active to present passive
English prompt: “The farmers carry the grain into the storehouse.” Transform it so “the grain” is the topic.
Choose transitive portant. Its object is neuter singular frūmentum; its subjects are agricolae. Motion into the building is in horreum with accusative. Promote frūmentum to nominative—the form looks the same because it is neuter—and make the verb singular passive portātur. Express the farmers as agent.
Frūmentum ab agricolīs in horreum portātur.
The grain is carried into the storehouse by the farmers.
Visible frūmentum could be nominative or accusative in isolation. The passive verb proves that it is the subject here. This is why parsing starts from the predicate, not from English order.
Worked prompt 2: perfect passive agreement
English prompt: “The queen sent two long letters to the commander.” Transform it so the letters become the topic.
The active skeleton is rēgīna duās epistulās longās ducī mīsit. Promote the feminine plural direct object to duae epistulae longae. Keep recipient ducī in the dative. The perfect passive participle is feminine plural missae, and the auxiliary is plural sunt.
Duae epistulae longae ducī ā rēgīnā missae sunt.
Two long letters were sent to the commander by the queen.
The agent can be omitted if attention belongs wholly to the letters: Duae epistulae longae ducī missae sunt.
A deliberately literal draft, revised
Prompt: “The wall was destroyed by fire.”
Sequential draft: Mūrus fuit dēlētus ab igne. This mechanically substitutes past fuit for English “was” and treats the nonpersonal cause “fire” like a human agent. The basic Classical perfect passive uses a participle with present sum for an event completed in the past, and a bare ablative can express the destructive means or cause.
Mūrus ignī dēlētus est.
The wall was destroyed by fire.
Perfect participle + fuit does occur in Latin as an alternative perfect, sometimes with contextual emphasis on completion or on a state that formerly held, so the draft is not impossible merely because of its auxiliary. It is not, however, the automatic equivalent of English simple “was destroyed.” Build the ordinary Latin perfect directly, and distinguish a nonpersonal cause from a personal agent.
Production and parsing diagnostics
For production, verify that the active verb has a promotable accusative object. Change that object to nominative, make every modifier agree, and rebuild the passive verb in the same tense and mood. Preserve datives and adverbials. Add ā/ab only for a personal agent; use a bare ablative for instrument or means. Finally, decide whether stating the agent serves the discourse.
For parsing, identify passive morphology first. Find a nominative that controls the verb or perfect participle; do not assume the first noun is an agent. Label ā/ab + ablative as a possible personal agent and test bare ablatives for instrument, means, cause, or another ablative function. With a neuter form, use verbal agreement and context because nominative and accusative may look identical.
Common Mistakes
1. Leaving the old object in the accusative
❌ Nautās ā duce laudantur.
Incorrect — accusative nautās cannot serve as the subject controlling laudantur.
✅ Nautae ā duce laudantur.
The sailors are praised by the commander.
With third-declension mīlitēs, nominative and accusative plural happen to look identical, so the corresponding change may be visible only in syntax. The promoted noun is still a nominative subject. First-declension nautae versus nautās makes the transformation overt.
2. Making the passive agree with the former agent
❌ Pōns ā mīlitibus mūniuntur.
Incorrect — plural mīlitibus is the agent, not the subject controlling the verb.
✅ Pōns ā mīlitibus mūnītur.
The bridge is fortified by the soldiers.
3. Using ab for an instrument
❌ Iānua ā clāvī aperta est.
Incorrect in the ordinary instrumental reading — a key is the means, not a personal agent.
✅ Iānua clāvī aperta est.
The door was opened with a key.
4. Forgetting participle agreement
❌ Epistulae missus sunt.
Incorrect — the participle must be feminine plural and the auxiliary spelling must remain plural.
✅ Epistulae missae sunt.
The letters were sent.
5. Copying the English auxiliary tense
❌ Lēx mūtāta erat.
Wrong for a simple perfect ‘the law was changed’: erat makes the Latin pluperfect, ‘had been changed.’
✅ Lēx mūtāta est.
The law was changed.
Key Takeaways
Promote the active accusative object to a nominative passive subject, then make the whole passive verb agree with it. Present-system passives are synthetic; perfect-system passives use an agreeing participle plus sum. Personal agents take ā/ab + ablative, instruments normally take the bare ablative, and other complements keep their functions. Transform only predicates whose Latin structure supports the passive; recast deponents and recognize impersonal passives as a separate pattern.
Now practice Latin
Reading grammar gets you part of the way. The exercises are where it sticks — free, no signup needed.
Start learning Latin →Related Topics
- Direct to Indirect StatementB1 — Turn a direct assertion into Classical Latin accusative-and-infinitive while preserving reference and relative time.
- Active and Passive VoiceA1 — Understand how Latin changes verb endings and clause structure to present a participant as actor or receiver of an action.
- Present Passive IndicativeA2 — Form the synthetic present passive across all conjugations and interpret its subjects, agents, and contextual values.
- Perfect-System Passive FormsA2 — See the perfect, pluperfect, and future perfect passive as one system built from an agreeing participle and forms of sum.
- Ablative of AgentA2 — Identify the deliberate personal agent of a passive action with ā or ab plus the ablative.
- Impersonal Passive ConstructionsA2 — Recognize subjectless third-person singular passives and translate the activity naturally instead of inventing a nominative subject.