With a verb like 쓰다 (to write, to use) the standard polite conjugation will be 써요 in the present tense. To form the standard polite ending of 으 ending verbs, drop the 다, like the 다 in 쓰다 and change the 으 vowel in 쓰다 to an 어 vowel. Now try conjugating the adjective 크다 (to be big) in the standard polite. If you follow the instructions above, it’ll be 커요. To form the past tense of 쓰다, drop the 다, change it to a 어 vowel and add 써어요 to the stem. So the past tense of 쓰다 is 썼어요. Now try conjugating the past tense of 크다. You’ll get 컸어요.

To form the deferential polite of 쓰다 in the present tense, add ㅂ니다 to the stem. So 쓰다 in the deferential polite will be 씁니다. The same goes for 크다. It’ll be 큽니다 in the deferential polite. To form the deferential polite past tense of 쓰다, add ㅆ습니다 to the stem and change the 으 vowel to a 어 vowel. So 쓰다 will be 썼습니다. For 크다, the past tense of the deferential polite will be 컸습니다. To form the honorific deferential in the present tense, add 십니다 to the stem. So 쓰다 will be 쓰십니다 and 크다 will be 크십니다 in the present tense of the honorific deferential.

In the honorific deferential past tense, 쓰다 will be 쎴습니다 and 크다 will be 크썼습니다 To form the honorific polite of 쓰다, add 세요 to the stem. So 쓰다 will be 쓰세요 in the honorific polite. Similarly, 크다 will be 크세요 in the honorific polite. In the past tense of the honorific polite, add 쎴어요 to the stem. So 크다 will be 크쎴어요 and 쓰다 will be 쓰쎴어요. Adjectives like 예쁘다 (to be pretty) will be conjugated in the same way. However, it’ll be a little different with adjectives like 바쁘다 (to be busy) and 나쁘다 (to be bad). Notice that 바쁘다 and 나쁘다 all have the 아 vowel.

(나 has the 아 vowel in 나쁘다 and 바 has the 아 vowel in 바쁘다) So 바쁘다 will be conjugated as 바빠요 instead of 바뻐요. The same goes for 나쁘다, it’ll be conjugated as 나빠요 instead of 나뻐요 in the standard polite. In the past tense of the standard polite, 나쁘다 will be 나빴어요 (not 나뻤어요) and 바쁘다 will be 바빴어요 (not 바뻤어요). Also, colloquially speaking, you may hear Korean people use 나뻐요/나뻤어요 and 바뻐요/바뻤어요. This is actually a common error that native speakers of Korean often make. For reference, the correct conjugation is 나빠요/나빴어요 and 바빠요/바빴어요.