Why is intereo not declined like habeo? I thought all verbs ending in -eo were second conjugation.

However, the 3rd person singular if habeo is habet, but the 3rd person singular of intereo is interit.

What is the explanation?


Intereō is a compound, inter-eō; the second part is the famous irregular verb eō, īre, ivī/iī, itus.

As such, it conjugates like eō does: inter-eō, inter-īs, inter-it, etc.

As for why eō acts like that—the stem was originally something like *ei- (*eiō *eire etc). But Latin generally didn't like sequences of three vowels in a row, so the first singular *eiō became eō; later, *ei became ī, giving a stem of ī- (*eis > īs, *eire > īre, etc) but leaving the first singular with an unexpected e-. Same with the third plural, since that ending also begins with a vowel: *eiont > *eont > eunt.

  • 1
    (Technically the older form of the infinitive should be *eise, but I'm ignoring rhotacism here since it's not relevant to the vowel discussion.)
    – Draconis
    Apr 24 at 2:29
  • Cf. iens, but euntes, eundum.
    – Cerberus
    Apr 24 at 14:49

Take a look at wiktionary's page for the word: it's īre, eō, īs...eunt...iē̆runt with an inter- stuck to its face. It shares one form with with the ē-conjugation by a pure accident, and in that form is the ending and e- < ei- is the stem (as in ī-re < ei-re) with no thematic vowel (the -ē- of habē-ō/s/t... which breaks/shortens if another vowel or final -t follows).

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