应该 yīnggāi
应该（yīnggāi）means “should / ought to: obligation or reasonable inference”. 应该 goes before a verb to say something is proper or expected — 'should, ought to. Formation: 应该 + 动词/形容词（否定：不应该）
should / ought to: obligation or reasonable inference
HSK2Formation
应该 + 动词/形容词（否定：不应该）
Explanation
应该 goes before a verb to say something is proper or expected — 'should, ought to.' It expresses either a duty (you should rest) or a confident guess (he should be there by now). The negative is 不应该 ('shouldn't').
Examples
Note
Negative 不应该 = 'should not'. In speech 应该 can be shortened to 该.
FAQ
应该 — what does it mean and how is it used?
should / ought to: obligation or reasonable inference. 应该 goes before a verb to say something is proper or expected — 'should, ought to.' It expresses either a duty (you should rest) or a confident guess (he should be there by now). The negative is 不应该 ('shouldn't').
应该 — how do you form it?
应该 + 动词/形容词（否定：不应该）
应该 — any usage notes?
Negative 不应该 = 'should not'. In speech 应该 can be shortened to 该.