Allomorphs

[zelos]

Quick question, why do languages tend to develop allomorphs such as first/second/third/etc declension as many languages have and more?

ar/er/ir verbs in spanish and more.

Does it only have to do with being easier to pronounce or something else?

[Legion]

It's more like regularization and extensions of patterns appearing because of sound changes that wreck havoc in an originally regular system.

For instance, the infinitive in Latin was originally just the -re part (from an earlier -se). Because of morpheme boundary accidents, the stem vowel, which was originally just the final vowel of the root, got increasingly reanalized as part of the ending, thus leading to different conjugations.

[Mecislau]

I don't really know if this was the case in PIE or not, but it could also be that the different conjugations (ie, different thematic vowels) actually had different meanings. Look at Slavic languages, were -i- verbs are prototypically causatives, -ě- verbs are statives or transformatives, and -a- verbs are imperfective.


(That's a total oversimplification, but my point is clear meanings tendencies can be assigned to the different thematic vowels)