For those who want to learn korean!!!
(info colected from several apps/books to make it as full and organized as possible)(all the credit to that apps/books)
If the last letter of a word stem ends in ㅅ (for example: 짓다 = to build), the ㅅ gets removed when adding a vowel. For example, when conjugating:
짓다 = to make/build ↘짓 + 어 = 지어 나는 집을 지어 = I build a house ↘짓 + 었어요 = 지었어요 ↘저는 집을 지었어요 = I built a house
Notice that this only happens when adding a vowel. When conjugating to the plain form, for example, you only add “는다” to the stem and thus ㅅ does not get removed:
집을 짓는다 = to build a house
The reason this irregular is done is to avoid changing the sound of a word completely after conjugating it. Pronouncing 짓다 sounds like ‘jit-da.’ Pronouncing 지어 sounds like ‘ji-uh’ Pronouncing 짓어 sounds like ‘jis-suh’
The third one (which is incorrect) completely changes the sound of the word stem when a vowel is added (from ‘jit’ to ‘jis.’ Whereas in the second one, the sound of the word stem only changes from ‘jit’ to ‘ji,’ which is much smaller of a difference (especially considering the ‘t’ in the pronunciation of 짓 is not aspirated - which makes it barely audible). I know that is confusing, but if you can’t understand why it is done, that’s fine. Just know that it must be done. Some other examples of words that follow this irregular are (these words are too difficult for you right now, but I'm just showing you):
낫다 = better (adjective) 잇다 = to continue (verb)
Common words that this does not apply to are:
웃다 (to laugh) = 저는 웃었어요 = I laughed 벗다 (to take off clothes) = 저는 저의 옷을 벗었어요 = I took off my clothes 씻다 (to wash) = 저는 저의 손을 씻었어요 = I washed my hands
Here is a table with the word “짓다 (to build)” being conjugated using all the honorific forms you have learned. 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.
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Note that when a word stem has ㅅ as the fourth consonant, this irregular does not apply. For example, this does not apply to 없다, which you will learn about later
ㄷ irregular
If the last letter of a word stem ends in ㄷ (걷다 = to walk), the ㄷ gets changed to ㄹ when adding a vowel. This is only done with verbs. 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 is simply stays as 걷어. In addition, 걸다 means “to hang.” When conjugating, by adding a vowel it stays as 걸어 Confusing enough? Let’s look at all three:
