1. Infinitives
Summary/Notes

2. The Infinitive is a mood of the verb
The Infinitive is a mood of the verb. (The other moods are: indicative, imperative, and subjunctive.)
Infinitives do NOT have person or number; in other words, they are not “limited” or “finite” as to the subject of the verb.
Infinitives DO have tense and voice.

3. The infinitive is a verbal noun
The infinitive is a verbal noun. It states the name of the action of the verb. It is considered to be neuter in gender and singular in number; so an adjective must agree with it in that gender and number. Ex.: “To love is good” = “Amare est bonum.”

4. The Second Principal Part of a verb is its present active infinitive.
There are six infinitive forms for all regular verbs. Some irregular or intransitive verbs have fewer than this.

5. How to form the infinitives
Active
Passive
Present
2nd principal part
“to verb”
2nd principal part; replace –re with –ri; for 3rd conjugation replace –ere with –i
“to be verbed”
Perfect
3rd principal part + -sse
“to have verbed”
4th principal part with “esse”
“to have been verbed”
Future
Future Active Participle with “esse”
“to be about to verb”
4th principal part with –um ending and “iri”
“to be about to be verbed”