Sentence form that simply states facts or opinions
When to use
stating facts, expressing opinions, conveying information
The nuance
Use 평서형 to convey information or express thoughts. Ends with declarative sentence endings like -다, -요, or -습니다.
평서형 (pyeong-seo-hyeong, pyeongseohyeong) · 의문형 (ui-mun-hyeong, uimunhyeong)
Pyeongseohyeong (declarative) expresses statements or opinions, while uimunhyeong (interrogative) is used to ask questions.

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Sentence form that simply states facts or opinions
When to use
stating facts, expressing opinions, conveying information
The nuance
Use 평서형 to convey information or express thoughts. Ends with declarative sentence endings like -다, -요, or -습니다.
Sentence form used to ask questions or seek responses from others
When to use
asking for information, requesting confirmation, inquiring about responses
The nuance
Use 의문형 to ask or confirm information from others. Ends with interrogative endings like -까?, -니?, or -나요?.
오늘 날씨가 좋다.
o-neul nal-ssi-ga joh-da., o neul nal ssi ga joh da.
Correct as a declarative sentence stating a fact.
오늘 날씨가 좋니?
o-neul nal-ssi-ga joh-ni?, o neul nal ssi ga joh ni?
Correct as an interrogative sentence asking a question.
너 어디 가?
neo eo-di ga?, neo eo di ga?
Correct interrogative sentence asking someone where they are going.
너 어디 가.
neo eo-di ga., neo eo di ga.
Incorrect because it is a statement form used where a question is intended.
저는 학생입니다.
jeo-neun hak-saeng-ip-ni-da., jeo neun hak saeng ip ni da.
Correct declarative sentence stating one's status.
저는 학생입니까?
jeo-neun hak-saeng-ip-ni-kka?, jeo neun hak saeng ip ni kka?
Correct interrogative sentence asking a question.
밥 먹었니?
bap meok-eoss-ni?, bap meok eoss ni?
Correct interrogative sentence asking if someone ate.
밥 먹었다.
bap meok-eoss-da., bap meok eoss da.
Correct declarative sentence stating a fact.
What sentence form is '오늘은 날씨가 어때요?'?
What sentence form is '나는 학생이다.'?
Which sentence form is used to ask someone for information?