Vergil’s Verb Tips: The Infinitive

If the verb form ends in . . .	. . . it’s this kind of infinitive:	... and is normally translated as follows: as follows:
-āre, -ēre, -ere, -īre, -esse (sum & compounds)	present active	to x
-ārī, -ērī, -ī^1, -īrī	present passive^2	to be x’ed
(3rd stem +) -isse; (nōsse for nōvisse)^3	perfect active^3	to have x’ed
-us/-a/-um (4th principal part)^4 + esse^5	perfect passive^6	to have been x’ed
(4th stem +) -ūrus/-a/-um^7 + esse^5; (fore)^8	future active	to be about to x
-um (neut. 4th principal part)^9 + -īrī	future passive^9	to be about to be x’ed

Notes

1. Third and third -iō conjugation verbs form the present passive infinitive by adding -ī directly to the stem, instead of -erī. Examples: tollō (“lift”) becomes tollī (“to be lifted”), even though the present active infinitive is tollere (“to lift”); caedō (“slaughter”) becomes caedī (“to be slaughtered), even though the present active infinitive is caedere (“to slaughter”).

2. All deponent verbs have present infinitives with these endings, but they are nonetheless active. Examples: moror (1st conjugation) has present infinitive morār ī, which is translated “to delay,” not “to be delayed”; prōgredior (3rd -iō) has present infinitive prōgredī, which is translated “to proceed,” not “to be proceeded,” which logically would not exist, anyway.

3. Verbs with third principal parts ending in -vī commonly undergo syncopation when forming the perfect active infinitive. Probably the most common example is nōsse (“to have found out,” hence, “to know”) instead of the longer nōvisse.

4. The table gives the nominative singular forms for the perfect passive participle (4th principal part). These forms could also be nominative plural, -ī/-ae/-a. In indirect statements, the accusative form of the perfect passive participle would be used instead: singular in -um/-am/-um, plural in -ōs/-ās/-a.

5. It is quite common in poetry to omit the esse, just as poets often omit forms of sum.

6. Again, the perfect infinitive of a deponent verb would look the same, but would nonetheless be translated actively. Example: morātus esse is translated “to have delayed,” not “to have been delayed.”

7. To form the future active participle, knock the -us/-a/-um off the 4th principal part and replace it with -ūrus/-ūra/-ūrum. The endings could also be nominative plural or accusative singular or plural as described in note 4.

8. For indirect statement, fore is normally used in place of futūrus esse as the future active infinitive of sum and its compounds, such as adfore.

9. This infinitive is extremely rare. The neuter 4th principal part is really the supine.