Quote Originally Posted by Seraph View Post
This is not irregular.
Technically, this is true -- one needs to distinguish between "truly irregular" verbs (believe it or not, some scholars would say that Russian has only four of them *) and "verbs whose conjugations are annoying and confusing to foreigners" (of which Russian has too many to count). But from a learner's perspective, a verb conjugation like that of мочь (я могу, ты можешь...) might as well be irregular, even though strictly speaking it's not.

* Or, to be more precise, there are only four "basic, unprefixed" irregular verbs, though you can form additional verbs (with the same irregular conjugations) by prefixing. These basic irregular verbs are:

есть ("to eat")
дать ("to give," perfective)
хотеть ("to want")
бежать ("to run," uni-directional)

However, examples such as идти having the past tense forms шёл, шла... aren't counted among these "irregular" verbs -- even though for all practical purposes идти would seem to qualify as "highly irregular."

So, Antonio, that's what Seraph was getting at in saying that these "mutating-consonant" verbs are not irregular.