An infinitive is a basic form of a verb that in English often is preceded by "to" and that serves as a noun or a modifier. In Latin, infinitives are rarely used to indicate purpose, but rather are most often used to express indirect speech (oratorio obliqua).
Latin Infinitive Basics
When you look up a Latin verb in a Latin-English dictionary, you will see four entries (principal parts) for most verbs. The second entry—usually abbreviated "-are," "-ere," or "-ire"—is the infinitive. More specifically, it's the present active infinitive, which is translated into English as "to" plus whatever the verb means. The vowel (a, e, or i) of the infinitive indicates which conjugation it belongs to.
Example of a dictionary entry for a verb in Latin:
Laudo, -are, -avi, -atus. Praise
The first entry in the dictionary entry is the present, active, singular, first-person form of the verb. Note the -o ending. Laudo "I praise" is a first conjugation verb and, therefore, has an infinitive ending in "-are." The entire present active infinitive of laudo is laudare, which translates into English as "to praise." Laudari is the present passive infinitive of laudo and means "to be praised."
Most verbs have six infinitives, which have tense and voice, including:
- Present active (to praise)
- Present passive (to have been praised)
- Perfect active (to have praised)
- Perfect passive (to have been praised)
- Future active (to be about to praise)
- Future passive (to be about to be praised)
Perfect Infinitives of Latin Verbs
The perfect active infinitive is formed from the perfect stem. In the example of a first conjugation verb, laudo, the perfect stem is found on the third principal part, laudavi, which is listed in the dictionary simply as "-avi." Remove the personal ending ("i") and add "isse"—laudavisse—to make the perfect active infinitive.
The perfect passive infinitive is formed from the fourth principal part—in the example, laudatus, plus "esse." The perfect passive infinitive is laudatus esse.
Future Infinitives of Latin Verbs
The fourth principal part also informs future infinitives. The future active infinitive is laudaturus esse and future passive infinitive is laudatum iri.
Infinitives of Conjugated Latin Verbs
In Latin, verbs are conjugated to indicate voice, person, number, mood, time, and tense. There are four conjugations, or verb inflection groups.
Infinitives of a first conjugation Latin verb include:
- Present active—amare (love)
- Present passive—amari
- Perfect active—amavisse
- Perfect passive—amatus esse
- Future active—amaturus esse
- Future passive—amatum iri
Infinitives of a second conjugation Latin verb include:
- Present active—monere (warn)
- Present passive—moneri
- Perfect active—monuisse
- Perfect passive—monitus esse
- Future active—moniturus esse
- Future passive—monitum iri
Infinitives of a third conjugation Latin verb include:
- Present active—regere (rule)
- Present passive—regi
- Perfect active—rexisse
- Perfect passive— rectus esse
- Future active— recturus esse
- Future passive—rectum iri
Infinitives of a fourth conjugation Latin verb include:
- Present active—audire (hear)
- Present passive—audiri
- Perfect active—audivisse
- Perfect passive—auditus esse
- Future active—auditurus esse
- Future passive—auditum iri
Interpreting the Infinitive
It may be easy to translate the infinitive as "to" plus whatever the verb is (plus whatever person and tense markers may be required), but explaining the infinitive isn't as easy. It acts as a verbal noun; therefore, it is sometimes taught alongside the gerund.
Latin Composition's Bernard M. Allen says that just under half of the time that an infinitive is used in Latin, it is in an indirect statement. An example of an indirect statement is: "She says that she is tall." In Latin, the "that" wouldn't be there. Instead, the construction would involve a regular statement—she says (dicit), followed by the indirect part, with the subject "she" in the accusative case followed by the present infinitive (esse):
Dicit eam esse altam.
She says (that) she [acc.] is [infinitive] tall [acc.].
Allen says that Charles E. Bennett's New Latin Grammar provides a rule for the tense of the infinitive that is only applicable to the present infinitive in an indirect statement. According to Bennett's rule:
"The Present Infinitive represents an act as contemporaneous with that of the verb on which it depends."
Allen prefers the following:
"In Indirect Statements the present infinitive represents an act as contemporaneous with the time of verb on which it depends. In other substantive uses it is merely a verbal noun, without any tense force."
Tense in Latin Complementary Infinitives
As an example of why tense is a difficult concept with present infinitives, Allen says that in Cicero and Caesar, a third of their present infinitives follow the verb possum "to be able." If you are able to do something, that ability precedes the time of the statement.
Other Uses of the Infinitive
An infinitive can also be used as the subject of a sentence. The subjective infinitive is found after impersonal expressions like necesse est, "it is necessary."
Necesse est dormire.
it is necessary to sleep.