Question

Irregular ㅂ → 오

Accepted Answer

The adjective 곱다 and the verb 돕다 are the only two special cases in which, when conjugated irregularly, ㅂ changes to 오 when (and only when!) followed by the principle beginning with -아/어~.

돕다 → 도와요, 돕습니다, 도와서, 도우면, 도우니까, 도운

곱다 → 고와요, 곱습니다, 고와서, 고우면, 고우니까, 고운

Important note: 곱다 can be conjugated regularly in its meaning different from 'pretty'.
곱다 → 곱아요, 곱습니다, 곱아서, 곱으면, 곱으니까, 곱은

There are cases when one word may have several meanings. The same irregular-looking word can be conjugated regularly and irregularly depending on the particular meaning it is used in. Below are the few examples of such words.

곱다 in the meaning of 'pretty/nice' is conjugated irregularly
곱- + -어/아~ → 고오- + -아~ → 고와~
영희는 손이 고왔어요.
Young-hee had pretty hands.

곱다 in the meaning 'stiff/numb (with cold)' is conjugated regularly:
곱- + -아/어~ → 곱아~
찬물에 빨래를 하고 나니 손이 곱았어요.
My hands got stiff after washing the clothes in cold water.

굽다 in the meaning 'to grill' is conjugated irregularly:
굽- + -아/어~ → 구우- + -어~ → 구워-
고기를 구웠어요.</p>
I grilled the meat.

굽다 in the meaning 'to bend/curve' or 'to be crooked/bent' is conjugated regularly:
굽- + -아/어~ → 굽어~
(나이가 들어) 허리가 굽었어요.
I got bent with age.

I grilled the meat.굽다 in the meaning 'to bend/curve' or 'to be crooked/bent' is conjugated regularly:굽- + -아/어~ → 굽어~(나이가 들어) 허리가 굽었어요.I got bent with age.

Conjugated 곱다 Meaning 아/어~ 오 돕다 Cases 곱습니다