Erzya verbs are inflected for tense and mood, and are further conjugated for person of subject and object. Traditionally, three stem types are distinguished: "a"-stems, "o"-stems and "e"-stems. "A"-stems always retain the stem vowel "a" in the non-third person present tense forms, and in the third person first past tense forms (e.g. "pala-ś" "kissed"). With many "o"-stems and "e"-stems, the stem vowel is dropped in these forms (e.g. "o"-stem "van-ś" "watched", "e"-stem "ńiľ-ś" "swallowed"), but there also "o"- and "e"-stem verbs which retain the vowel ("udo-ś" "slept", "piďe-ś" "cooked"). Rueter (2010) therefore divides verb stems into vowel-retaining stems and vowel-dropping stems.