1.You ought to take care of him.
2.You ought to scrap the old bike and buy a new one.
3.You ought to have a haircut.
He must be at home by now. （断定他已到家）
He ought to be home by now. （不十分肯定）
This is where the oil must be. （比较直率）
This is where the oil ought to be. （比较含蓄）
三、“ought to + have + 过去分词”表示过去应做某事而实际未做。如：
You ought to have asked him (but you didn't).
Ought you smoke so much?
You oughtn't smoke so much.
ought属正式用语。由于ought to 没有过去式，所以在直接引语变间接引语的过程中，就不再变化.例如：
1.She failed one of the exam papers, but we ought to make allowance for the fact that she was ill.
2.Regularity ought to be observed, as regularity is very conducive to health.
3.China ought to make a greater contribution to humanity.
4.He is a very good tennis player; you ought to see him in action.
5.I think there's a train at 8.20 but you ought to make certain.
6.I think you ought to go to/to go and see the doctor.