LEARN KOREAN (한국어) [GRAMMAR] #1

ㄷ IRREGULAR

If the last letter of a word stem ends in ㄷ (for example: 걷다 - to walk), the ㄷ gets changed to ㄹ when adding a vowel. This is only done with verbs (I can't think of any adjectives where this must be done). For example:

걷다 - to walk
걷 + 어 - 걸어
저는 걸어요 - I walk

걷 - 었어요 - 걸었어요
저는 걸었어요 - I walked

I don't mean to confuse you, but I will:
걷다 means "to walk." When conjugating, by adding a vowel it changes to 걸어.

Another meaning of 걷다 is "to tuck." But this meaning of 걷다 does not follow the irregular rule. So when conjugating by adding a vowel, it simply stays as 걷어.

걸다 means "to hang." When conjugating, by adding a vowel it stays as 걸어.

Confusing enough? Let's look at all three:

Honestly, though, the whole 걷다/걷다/걸다 thing is probably the most confusing part of this conjugation, and don't worry too much about it. "Walk" is a word that is used much more frequently than "tuck," so don't worry about it too much.

The reason this conjugation is done is simply because the sounds flows off your tongue better. It is similar to pronouncing the word "butter" in English. When pronouncing "butter" we don't say "butt-tter," we just say "bud-er." Like the ㄷ irregular, it is simply to avoid saying a hard consonant.

This is done to most stems ending in ㄷ. Common words that this does not apply to (like 걷다 - to tuck) are:

받다 (to get/receive):
돈을 받았어요 - I received money

묻다 - 묻어요 (to bury):
저는 저의 강아지를 묻었어요 - I buried my dog

닫다 = 닫아요 (to close):
저는 문을 닫았어요 - I closed the door

Here is a table with the word "걷다 (to walk)" being conjugated using all the honorific forms you have learned so far. The irregular conjugations are in bold. Notice that this only occurs when ~아/어 (or one of its derivatives like ~았/었어요) is added to the verb stem.