The dictionary form and how 요-forms are built

Every verb has a dictionary form ending in 다

You know 먹어요, 읽어요, 가요 and 해요 as whole words. In a dictionary they are listed differently: 먹다, 읽다, 가다, 하다. Each one ends in 다.

Take 다 away and what is left — 먹, 읽, 가, 하 — is the stem. The stem carries the meaning; everything else is an ending attached to it. From here on you build the forms yourself instead of memorising each one.

The dictionary form is for looking words up. In conversation you keep using the 요-forms.

Look at the stem’s last vowel: 아요 or 어요

살 + 아요 = 살아요 (live). 놀 + 아요 = 놀아요 (play, hang out). But 먹 + 어요 = 먹어요, and 열 + 어요 = 열어요 (open).

The choice depends on the last vowel of the stem. If it is ㅏ or ㅗ, add 아요. If it is any other vowel, add 어요. The consonants around the vowel do not matter. This is the polite present ending, and the same choice returns in almost every form you will learn.

The rule holds whatever follows the vowel

닫 + 아요 = 닫아요 (close). 앉 + 아요 = 앉아요 (sit): two final consonants, but the vowel is still ㅏ. 쉬 + 어요 = 쉬어요 (rest): ㅟ is neither ㅏ nor ㅗ, so 어요.

In speech the final consonant links to the ending as usual: 닫아요 sounds like [다다요], and 앉아요 like [안자요]. Spelling keeps the stem intact so you can always see which verb it is.

하다 always becomes 해요

하다 → 해요. 공부하다 → 공부해요. 운동하다 → 운동해요 (exercise). 요리하다 → 요리해요 (cook).

하 has the vowel ㅏ, so you might expect 아요. It is the one verb that ignores the vowel rule: 하다 turns into 해요, every time. Hundreds of Korean verbs are a noun plus 하다 — 요리 is the noun “cooking” you met in unit 1 — and all of them work this way.

When the stem ends in a vowel, the two merge

가 + 아요 = 가요. 오 + 아요 = 와요. 보 + 아요 = 봐요. 마시 + 어요 = 마셔요. This is where the forms you have used since unit 2 come from.

The vowel rule is unchanged; only the spelling is shortened. ㅏ + 아 stays ㅏ, ㅗ + 아 becomes ㅘ, ㅜ + 어 becomes ㅝ, ㅣ + 어 becomes ㅕ. Two new verbs follow the same pattern: 배우다 → 배워요 (learn) and 기다리다 → 기다려요 (wait for).