Verbseoul.
하다 verb (adj)
확실하다hwaksilhadato be certain or definite

To say to be certain or definite politely in the present tense, use 확실해요 (hwahg-sheel-hae-yoh). Below is the full conjugation of 확실하다 across the three tenses and three everyday speech levels.

Conjugation table

TenseCasual (반말)Polite (요)Formal (합니다)
Present
확실해
hwahg-sheel-hae
확실해요
hwahg-sheel-hae-yoh
확실합니다
hwahg-sheel-hahm-nee-dah
Past
확실했어
hwahg-sheel-hae-ssuh
확실했어요
hwahg-sheel-hae-ssuh-yoh
확실했습니다
hwahg-sheel-hae-sseum-nee-dah
Future
확실할 거야
hwahg-sheel-hahl- -guh-yah
확실할 거예요
hwahg-sheel-hahl- -guh-yae-yoh
확실할 겁니다
hwahg-sheel-hahl- -guhm-nee-dah

Other useful forms

Command Polite (세요)
확실하세요
hwahg-sheel-hah-sae-yoh
Suggestion / Let's Polite (요)
확실해요
hwahg-sheel-hae-yoh
Question Polite (요)
확실해요?
hwahg-sheel-hae-yoh-?
Connective “and” — (고)
확실하고
hwahg-sheel-hah-goh
Conditional “if” — (면)
확실하면
hwahg-sheel-hah-myuhn
Noun form — (기)
확실함
hwahg-sheel-hahm