Latin complementary infinitives — Classical languages, 14–17
See how an infinitive completes verbs such as can, want and must. It is not a hidden quotation: it finishes the action that the first verb leaves open.
One verb opens the action
Some Latin verbs feel unfinished without another verb: possum means “I can”, but can do what? The infinitive supplies that missing action, as in possum currere, “I can run”. Both verbs belong to the same subject unless the sentence signals something else.
Why Latin uses an infinitive here
The problem is that English and other languages often use a marker such as “to”, while Latin can show the link through the infinitive itself. After verbs of ability, intention, beginning or duty, the infinitive keeps the second action closely attached to the first.
From debeo to “I must leave”
Start with debeo, “I owe” or “I must”, and discedere, “to leave”. The first-person ending -o tells you the subject is “I”; the infinitive names the required action. Debeo discedere therefore means “I must leave”, not “I owe leaving”.
Do not invent a second subject
You may expect every verb to bring its own subject, especially because an infinitive has no person ending. That is reasonable, but in possum videre the hidden subject of videre is still “I”. Look first for a noun or pronoun that could make the infinitive’s subject different.
Instructions and plans
This pattern appears whenever someone says what they can, want, dare or have to do: a plan, a rule, a promise or a warning. It also helps you read mottos such as sapere aude, “dare to know”, where the infinitive carries the action after a verb of daring.
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