This may have been asked before because it seems like something I would have wondered, had I ever learned German via textbook. But I couldn't find it, so I'm asking. Also, I am not sure if such a discussion is meant for this community. I hope it is.
More to the point: The present tense second plural form of "sein" is "(ihr) seid". Now if we look at the same form but in past tense it turns to "(ihr) wart".
The usage of "-t" at the end seems to be the regular way, since many other verbs (including some irregular ones) use it (both in present and past tense):
- laufen -> (ihr) lauft -> (ihr) lieft
- sagen -> (ihr) sagt -> (ihr) sagtet
- kochen -> (ihr) kocht -> (ihr) kochtet
- werden -> (ihr) werdet -> (ihr) wurdet
- gehen -> (ihr) geht -> (ihr) gingt
There is one obvious possible reason for using "(ihr) seid", which is that "seit" has a different meaning. But I was wondering: is there a different reason for this irregularity? Especially noting that words with double meaning have not thoroughly been removed from the language elsewhere.
As an extension, the question arises: why was the present tense changed (irregularly), but this irregularity was not kept through the other tenses (c.f. "wart")? I fear this could fall into the same category, as "ward" at least historically had been used differently (as the past tense of "werden").