Verbseoul.
하다 verb (adj)
마땅하다mattanghadato be suitable, to be appropriate, to be right

To say to be suitable, to be appropriate, to be right politely in the present tense, use 마땅해요 (mah-ttahng-hae-yoh). Below is the full conjugation of 마땅하다 across the three tenses and three everyday speech levels.

Conjugation table

TenseCasual (반말)Polite (요)Formal (합니다)
Present
마땅해
mah-ttahng-hae
마땅해요
mah-ttahng-hae-yoh
마땅합니다
mah-ttahng-hahm-nee-dah
Past
마땅했어
mah-ttahng-hae-ssuh
마땅했어요
mah-ttahng-hae-ssuh-yoh
마땅했습니다
mah-ttahng-hae-sseum-nee-dah
Future
마땅할 거야
mah-ttahng-hahl- -guh-yah
마땅할 거예요
mah-ttahng-hahl- -guh-yae-yoh
마땅할 겁니다
mah-ttahng-hahl- -guhm-nee-dah

Other useful forms

Command Polite (세요)
마땅하세요
mah-ttahng-hah-sae-yoh
Suggestion / Let's Polite (요)
마땅해요
mah-ttahng-hae-yoh
Question Polite (요)
마땅해요?
mah-ttahng-hae-yoh-?
Connective “and” — (고)
마땅하고
mah-ttahng-hah-goh
Conditional “if” — (면)
마땅하면
mah-ttahng-hah-myuhn
Noun form — (기)
마땅함
mah-ttahng-hahm