Active Infinitives
Infinitives are the Latin verb forms that are translated "to verb." Similar to verb tenses, there are past, present, and future infinitives. The most present infinitive forms are also the second principle parts of verbs.
Forming Infinitives
Present
To form the present infinitive for a verb, you simple take the second principle part of that verb. The present infinitives express actions that take place at the same time as the main action.
Past
To form the past infinitive for a verb, you take the third principle part, remove the -ī and add the letters -isse to the end. Past infinitives express actions that took place before the main action.
Future
To form the future infinitive for a verb, take the fourth principle part, add the letters -ur before the -um and "esse" as a separate word after it. Future infinitives express actions that will take place in the future.