From earlier, and still dialectally attested,mes (with vowel lengthening, either expressively, or under the influence ofjūs(“you pl.”)), fromProto-Balto-Slavic*mes, fromProto-Indo-European*wéy(“we”), with the initial m- appearing (whence*mey) due to influence from the first-person singular objective pronoun or the first-person singular verbal ending.
For the non-nominative forms, the oldProto-Indo-European*nos was not conserved; new forms were created, following the second-person plural paradigm. Accusativemūs imitated second-personjūs (i.e.,*múns afterjúns, yieldingmūs); similarly genitive*mūsōn after*jūsōn, yieldingmūsu, and dativemums <*mumus, parallelingjums <*jumus. Cognates includeLithuanianmẽs,Old Prussianmes,mas,Proto-Slavic*my,Old Armenianմեք(mekʻ).[1]
mēs(personal, 1st person plural)
| singular | plural | ||
|---|---|---|---|
| 1st person | es | mēs | |
| 2nd person | familiar | tu | jūs |
| polite | jūs | ||
| 3rd person | m | viņš | viņi |
| f | viņa | viņas | |