From what I read here and there, it is in fact the 4th conjugation that is irregular while ire
has kept the regular/original forms. Originally the imperfect and the future of 4th conjugation verbs was in -b-
like the 1st and 2nd conjugation but at some point (and surely because of their common ending -io
), they began to "borrow" forms from the -io
verbs of the 3rd conjugation.
This explains that, for some verbs, "irregular" forms can sometimes be found :
instead of audiam
instead of audiebam
. XIV, 37)
- see also here
for references to "irregular" forms of verbs based on eo
Disclaimer. This is based mainly on what I read here
but I am not sure I understood all of this correctly (and maybe research on Indo-european has modified this conception during the last century), please correct me if this is the case.