The Latin Infinitive — All Six Forms and the Tense Relationship in the ACI
The Latin infinitive has — unlike in English — six forms: three time stages (present, perfect, future) in both active and passive. It matters most in the ACI (accusative and infinitive), where the choice of infinitive is decisive: it fixes the tense relationship to the main action. This article is part of the Learn Latin section of Lapicida.
- 6 infinitive forms: present, perfect, future × active and passive
- Tense relationship in the ACI: simultaneous, anterior, posterior
- Forming the future passive infinitive: supine + iri (rare)
- Common mistakes: the accusative subject and the relative tense relationship
Which infinitive forms does Latin have?
Latin has six infinitives: present active (-re), present passive (-ri / -i for consonant-stem verbs), perfect active (-isse), perfect passive (PPP + esse), future active (FAP + esse) and future passive (supine + iri). In the ACI the infinitive expresses the tense relationship to the main verb.
| Infinitive | Active (amare) | Passive (amari) | Tense relationship in the ACI |
|---|---|---|---|
| Present | amare | amari | simultaneous |
| Perfect | amavisse | amatum esse | anterior |
| Future | amaturum esse | amatum iri | posterior |
Forming the six infinitive forms
Present active infinitive: present stem + -re: amare, monere, legere, audire. For consonant-stem verbs of the 3rd conjugation: stem + -ere.
Present passive infinitive: present stem + -ri: amari, moneri, audiri. Exception: consonant-stem verbs (3rd conj.) end in -i: legi, capi.
Perfect active infinitive: perfect stem + -isse: amavisse, monuisse, legisse, audivisse.
Perfect passive infinitive: PPP + esse: amatum esse, monitum esse. The PPP agrees with the accusative subject of the ACI.
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Future active infinitive: FAP (future active participle) + esse: amaturum esse. The FAP agrees with the accusative subject of the ACI.
Future passive infinitive: supine (ending in -um) + iri: amatum iri. This form is rare in classical Latin.
| Form | Ending / formation | Example (amare) |
|---|---|---|
| Pres. act. | stem + -re | amare |
| Pres. pass. | stem + -ri | amari |
| Perf. act. | perf. stem + -isse | amavisse |
| Perf. pass. | PPP + esse | amatum esse |
| Fut. act. | FAP + esse | amaturum esse |
| Fut. pass. | supine + iri | amatum iri (rare) |
The tense relationship in the ACI: simultaneous, anterior, posterior
The ACI (accusative and infinitive) is a clause-like construction that follows verbs of saying, thinking and perceiving. The tense relationship of the infinitive is always relative to the main verb — not absolute. There is more on ACI structure in the article the Latin ACI in the Lapicida Learn Latin section.
Simultaneity (present inf.): the ACI action happens at the same time as the main action. Caesar dicit milites pugnare. (Caesar says that the soldiers are fighting.) — fighting = simultaneous with ‘says’.
Anteriority (perfect inf.): the ACI action is completed before the main action. Caesar dicit milites pugnavisse. (Caesar says that the soldiers have fought.) — have fought = before ‘says’.
Posteriority (future inf.): the ACI action lies after the main action. Caesar dicit milites pugnâturos esse. (Caesar says that the soldiers will fight.) — will fight = after ‘says’.
The infinitive is the basis for the ACI and the NCI — the Latin grammar overview shows all the related constructions in one place.
| Infinitive | Tense relationship | Example | Translation form |
|---|---|---|---|
| Present active | simultaneous | pugnare | that they are fighting |
| Perfect active | anterior | pugnavisse | that they have fought |
| Future active | posterior | pugnâturos esse | that they will fight |
Train the ACI and the infinitive forms in the sentence quiz
Common mistakes with the Latin infinitive
- Translating the accusative subject as a nominative: in the ACI the subject of the infinitive stands in the accusative. Caesarem pugnare = that Caesar is fighting (not: Caesar is fighting).
- Ignoring the tense relationship: pugnavisse does not mean ‘they fought’ (an absolute past), but ‘that they have fought’ (relative to the main verb).
- Confusing se and eum in the ACI: the reflexive se refers back to the subject of the main clause — Marcus dicit se venire = Marcus says that he (himself) is coming; whereas eum/eam refers to a different person — Marcus dicit eum venire = Marcus says that he (someone else) is coming.
- Overlooking the future infinitive: amaturum esse is often misread as PPP + esse. You can spot the FAP by the ending -turus/-tura/-turum.
- Forgetting PPP agreement in the perfect passive infinitive: the PPP in amatum esse agrees with the accusative subject: with a feminine subject, amatam esse.
- Forming the future passive infinitive wrongly: not FAP + iri, but supine (ending in -um) + iri: amatum iri.
In the original: Cicero puts the infinitive as a subject in a nutshell: „vivere est cogitare” — “to live is to think” (Cicero, Tusculanae). Here the infinitive vivere works just like a noun.
Frequently asked questions — the Latin infinitive
How do I recognise the perfect active infinitive?
The perfect active infinitive always ends in -isse: amavisse, legisse, audivisse. It is formed from the perfect stem (3rd principal part minus -i, plus -isse). In the ACI it signals anteriority to the main verb.
What does ‘relative tense relationship’ mean in the ACI?
The tense relationship of the infinitive is always measured against the main verb — not against an absolute point in time. Present infinitive = simultaneous, perfect infinitive = before the main verb, future infinitive = after the main verb. This holds regardless of whether the main verb is present, perfect or imperfect.
After which verbs does the ACI stand?
After verbs of saying (dicere, narrare, nuntiare), thinking (putare, credere, existimare), perceiving (videre, audire, sentire) and willing (iubere, vetare). The ACI also follows scire (to know).
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About the author
Andreas Blankenstein is the founder of Lapicida Latinus — and dyslexic himself. When he had to catch up on his Latinum in record time, one thing became clear: endless table-cramming fails exactly the people who learn differently. That is why Lapicida trains grammar in the context of real authorial texts, colour-coded and in short steps. More about Andreas and the Lapicida method →
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