Third Conjugation Regular vs. “-io”

In Latin, there are two main subgroups of verbs that fall under the third conjugation: regular third conjugation verbs and third "-io" conjugation verbs. The “-io” refers to the ending of the verb’s first principle part. While both belong to the broader third conjugation, they differ in their endings.

Regular Third Conjugation

Regular third conjugation verbs typically have an infinitive ending in -ere. A regular third conjugation verb will also have an “-ō” as the ending to its first principle part.

The present tense endings for regular third conjugation verbs are as follows:

  • -ō (I) 

  • -is (You)

  • -it (He/she/it)

  • -imus (We)

  • -itis (You all)

  • -unt (They)

Third "-io" Imperfect (facere)

  • faciēbam

  • faciēbās

  • faciēbat

  • faciēbāmus

  • faciēbātis

  • faciēbant

Third "-io" Conjugation

The third "-io" conjugation, also known as the i-stem or io-stem conjugation, is a subgroup within the broader third conjugation. These verbs have an infinitive ending in -ere, just like regular third conjugation verbs.

Present Tense: The present tense endings for third "-io" conjugation verbs are different from regular third conjugation verbs. The first-person singular ending is "-io" instead of -ō. For example, "capere" (to take) and "facere" (to make) are third "-io" conjugation verbs.

  • -iō (I) 

  • -is (You)

  • -it (He/she/it)

  • -imus (We)

  • -itis (You all)

  • -unt (They)

It is important to note that because the “i” is included in third “-io” verbs’ present stem it is also included in any tenses based on the present stem, including imperfect and future.

Third "-io" Future (facere)

  • faciam

  • faciēs

  • faciet

  • faciēmus

  • faciētis

  • facient