Summary: Please look at my The Korean (Ir)regular Verbs.
Almost all languages that have conjugations (verb modifications) also have irregular verbs (Turkish being the only exception I’m aware of). English has verbs like “to write – wrote – written”; French has “écrire – j’écris – j’écrivais – écrit” and there is no shortage of examples from other languages.
Irregular verbs are a burden on language learners, but often there is help. Any self-respecting English dictionary has a list of the 300+ irregular verbs in the back, and for French there is a useful little booklet “Bescherelle La conjugaison pour tous” (“Conjugation for Everybody”), which for less than 7 euro’s explains everything there is to know about the French verb.
No such list or booklet seems to exists for Korean. There may be one in Korean, but with my present level of Korean (just passed my Beginners 2 test), it would be pretty useless to me anyway. There is the Web site Dongsa, which will conjugate any Korean verb for you, but it does not distinguish between regular and irregular, nor does it give any rules. And the rest of my learning material, from the simplest 50-page leaflets to the most solid and extensive 500-page works are all sketchy at best on the subject. I suppose if you’re a person who reads the 50-page leaflets you’re too junior to be interested in irregular verbs, and if you read the 500-page works you’re too senior to worry about them. Me, I’m in between, and confused.
In my The Korean (Ir)regular Verbs I’ve tried to cover the Korean verb with the same thoroughness as the Bescherelle does for French. I have collected material from all sources available to me, cross-checked and tested in Internet searches. I think it is over 95% complete, but that’s just a guess.
A bit about the irregularity of Korean irregular verbs:
Usually the irregular verbs of a language are a jumble; it’s more or less every verb for itself. English “to write – wrote – written” does not lead to “to bite – bote – bitten”; it may be related to “to ride – rode – ridden” but that is already running thin.
Not so in Korean. All irregular Korean verbs fall neatly in 6 groups, depending on the last consonant of the stem. So where is the irregularity? Answer: not all verbs that seem to fall into these groups are actually irregular. For example, all irregular verbs in -ㅂ (-p) are irregular in the same way, but not all verbs in -ㅂ are irregular. So when you see a verb in -ㅂ you know it might be irregular, and if it is irregular you know how to conjugate it, but you still don’t now whether it’s irregular or not. This means that for the language learner each group should come with a list of verbs that belong to it and a list of verbs that look as if they belong but don’t. In all learning material I have these lists are sketchy and by example only. I try to provide the complete lists.