ㄷ irregular verbs

Many verbs/adjectives with a ㄷ 받침 are irregular:
the ㄷ changes to ㄹ when followed by a vowel.
Note that many verbs/adjectives with a ㄷ 받침 are regular (the ㄷ does not change).
There is no specific rule to know whether one is irregular or not; instead you must memorize which are irregular and which ones aren't.

Explanation

For irregular ㄷ verbs, no change is made to the 받침 if ...it is followed by a consonant.
For example:
듣다 → 듣습니다
For irregular ㄷ verbs, the ㄷ 받침 changes to a ㄹ when followed by a vowel.
For example:
듣다 → 들어요

Steps for conjugating irregular ㄷ verbs which are followed by a vowel:
1. Replace ㄷ 받침 with ㄹ
2. Follow the same conjugation rules for patterns with a 받침.
For example:
걷다 + A/V + (으)니까 you would use 으 since it has a 받침.
So 걷다 becomes 걸으니까

Note that ㄹ irregular verbs, verbs with a ㄹ 받침 are irregular in a different way. (This can be somewhat confusing if you mix them up with ㄷ irregular verbs.)

Irregular Verbs

Conjugation Examples for Irregular Verbs
걷다 (to walk) ☞걷습니다 ☞ 걸어요 ☞ 걸었어요 ☞ 걸을 거예요 ☞걸으니까 ☞ 걸으면 ☞걸으세요

깨닫다 (to perceive, to realize) ☞ 깨닫습니다 ☞ 깨달아요 ☞ 깨달았어요 ☞ 깨달을 거예요 ☞ 깨달으니까 ☞ 깨달으면 ☞ 깨달으세요

듣다 (to listen) ☞ 듣습니다 ☞ 들어요 ☞ 들었어요 ☞ 들을 거예요 ☞ 들으니까 ☞ 들으면 ☞ 들으세요

묻다 (to ask) ☞ 묻습니다 ☞ 물어요 ☞ 물었어요 ☞ 물을 거예요 ☞ 물으니까 ☞ 물으면 ☞ 물으세요

싣다 (to load) ☞ 싣습니다 ☞ 실어요 ☞ 실었어요 ☞ 실을 거예요 ☞ 실으니까 ☞ 실으면 ☞ 실으세요

Regular Verbs

These verbs are not affected by the rules of irregular verbs and are conjugated normally.
Conjugation Examples for Regular Verbs

믿다(to trust, believe) ☞ 믿습니다 ☞ 믿어요 ☞ 믿었어요 ☞ 믿을 거예요 ☞ 믿으니까 ☞ 믿으면 ☞ 믿으세요

닫다(to close) ☞ 닫습니다 ☞ 닫아요 ☞ 닫았어요 ☞ 닫을 거예요 ☞ 닫으니까 ☞ 닫으면 ☞ 닫으세요

받다(to receive) ☞ 받습니다 ☞ 받아요 ☞ 받았어요 ☞ 받을 거예요 ☞ 받으니까 ☞ 받으면 ☞ 받으세요

얻다(to receive) ☞ 얻습니다 ☞ 얻어요 ☞ 얻었어요 ☞얻을 거예요 ☞ 얻으니까 ☞ 얻으면 ☞ 얻으세요

묻다(to bury) ☞ 묻습니다 ☞ 묻어요 ☞ 묻었어요 ☞ 묻을 거예요 ☞ 묻으니까 ☞ 묻으면 ☞ 묻으세요

쏟다(to pour) ☞ 쏟습니다 ☞ 쏟아요 ☞ 쏟았어요 ☞ 쏟을 거예요 ☞ 쏟으니까 ☞ 쏟으면 ☞ 쏟으세요

내닫다(to run away suddenly)
내리닫다 (run down, leap down