Verbseoul.
하다 verb (adj)
당연하다dangyeonhadato be reasonable or natural

To say to be reasonable or natural politely in the present tense, use 당연해요 (dahng-yuhn-hae-yoh). Below is the full conjugation of 당연하다 across the three tenses and three everyday speech levels.

Conjugation table

TenseCasual (반말)Polite (요)Formal (합니다)
Present
당연해
dahng-yuhn-hae
당연해요
dahng-yuhn-hae-yoh
당연합니다
dahng-yuhn-hahm-nee-dah
Past
당연했어
dahng-yuhn-hae-ssuh
당연했어요
dahng-yuhn-hae-ssuh-yoh
당연했습니다
dahng-yuhn-hae-sseum-nee-dah
Future
당연할 거야
dahng-yuhn-hahl- -guh-yah
당연할 거예요
dahng-yuhn-hahl- -guh-yae-yoh
당연할 겁니다
dahng-yuhn-hahl- -guhm-nee-dah

Other useful forms

Command Polite (세요)
당연하세요
dahng-yuhn-hah-sae-yoh
Suggestion / Let's Polite (요)
당연해요
dahng-yuhn-hae-yoh
Question Polite (요)
당연해요?
dahng-yuhn-hae-yoh-?
Connective “and” — (고)
당연하고
dahng-yuhn-hah-goh
Conditional “if” — (면)
당연하면
dahng-yuhn-hah-myuhn
Noun form — (기)
당연함
dahng-yuhn-hahm