Same Spelling, Different Behavior
You might think that all verbs ending in the same bottom consonant (받침) follow the same rules.
However, Korean has both regular and irregular words that share the exact same final consonant .
This means you cannot always predict if a word is irregular just by looking at its dictionary form.
The ㄷ and ㅂ Consonant Pairs
Let's compare words ending in ㄷ and ㅂ .
The ㄷ Consonant
Dictionary Form · Conjugated Form · Type
듣다 · 들어요 · Irregular
받다 · 받아요 · Regular
For 듣다 , the ㄷ changes to ㄹ before a vowel. But for 받다 , the ㄷ remains.
The ㅂ Consonant
Dictionary Form · Conjugated Form · Type
춥다 · 추워요 · Irregular
입다 · 입어요 · Regular
For 춥다 , the ㅂ changes to 우. But for 입다 , the ㅂ remains.
The ㅅ and ㅎ Consonant Pairs
Now let's look at words ending in ㅅ and ㅎ .
The ㅅ Consonant
Dictionary Form · Conjugated Form · Type
짓다 · 지어요 · Irregular
웃다 · 웃어요 · Regular
For 짓다 , the ㅅ drops before a vowel. But for 웃다 , the ㅅ remains.
The ㅎ Consonant
Dictionary Form · Conjugated Form · Type
빨갛다 · 빨개요 · Irregular
좋다 · 좋아요 · Regular
For 빨갛다 , the ㅎ drops and the vowel changes. But for 좋다 , the ㅎ remains.
Realistic Learning Strategy
Because you cannot always guess which words are regular and which are irregular by their spelling, you should learn the dictionary form and the conjugated form together.