Infinitive Mood
The infinitive is a verbal noun — neuter singular, no person, no number. Errāre est hūmānum — "to err is human": the infinitive sits as the subject of est, a noun made out of a verb.
But it only LOOKS like a noun. It keeps its verb-side too — takes adverbs, governs the same case as its finite form, has tense and voice.
That dual life drives every use: subject (errāre est hūmānum); object after verbs of saying with its own subject in the accusative (dīcit montem ab hostibus tenērī); the back half of possum, dēbeō, volō (possum venīre); a narrative tense in Sallust (the historical infinitive); and, in poetry, a tail of purpose where prose would write ut + subjunctive.
Learnings0 core · 1 AP claim
AP framework claims (1)— verbatim from AP CED
"to " / "to have ed" / "to be about to " — a verbal noun that still keeps tense, voice, and verb-government
Treat it as a noun for syntax (subject, object, predicate) but as a verb for what comes after it (adverbs, same case as the finite form).
| Case | Active | Passive |
|---|---|---|
| Present | amāre | amārī |
| Perfect | amāvisse | amātus esse |
| Future | amātūrus esse | amātum īrī |
See It In Action
— B. G. i. 22
Indirect statement, A&G's textbook example. Montem is accusative — the subject of tenērī — because the whole clause is the object of dīcit. English drops the accusative-with-infinitive shape and uses "that" + a finite verb.
— Sall. Cat. 21
Pure historical infinitive: Catiline (nominative!) is the subject, pollicērī a bare present infinitive doing the work of an imperfect. Sallust strings them together for a rapid, breathless catalogue — the form itself sounds urgent.
— Aen. i. 527
Poetic infinitive of purpose. In prose Vergil would have written ut populēmur with a subjunctive, but verse compresses the whole purpose clause into a single infinitive — a Greek-influenced shortcut Caesar would never use.
— Cic. Fam. xiv. 1
Exclamatory infinitive — no main verb, just acc. + inf. dropped in as a cry. Cicero writes this to his wife from exile; the bare construction makes the grief feel unsayable, as if the sentence couldn't bear to finish itself.
Both can act as nouns made from verbs, but Latin uses them in different slots — the infinitive is the verbal noun for subject and predicate; the gerund covers the oblique cases.
verbal noun for nominative + accusative; "to "
errāre est hūmānum
to err is human (subject of est)
verbal noun for genitive, dative, ablative, acc. with ad; " -ing"
ars amandī
the art of loving (genitive: amandī, not amāre)
Tip: Ask: what case do I need? Nominative or simple accusative → infinitive. Genitive (amandī), dative (amandō), ablative (amandō), or ad amandum → gerund. Latin avoids putting the infinitive in the oblique cases.
In Sallust's tum Catilīna pollicērī tabulās novās, what is pollicērī doing?
Study Tips
- •Spot the infinitive first by its endings: present active -re (amāre, vidēre, regere, audīre), present passive -rī / -ī (amārī, regī). Perfect active -isse (amāvisse). Future active -tūrum esse.
- •When you see dīcit, putat, sciō, audit (saying/thinking/perceiving), expect an accusative + infinitive — that's indirect statement, not a direct object plus a free-floating verb.
- •After possum, dēbeō, volō, soleō, audeō, incipiō, dēsinō, the infinitive completes the meaning: possum venīre = "I am-able to-come." No subject accusative — the doer is the same as the main verb's.
- •In Sallust and Tacitus, a stream of bare infinitives in narrative is the historical infinitive — translate as imperfect indicative: Catilīna pollicērī = "Catiline kept promising."