Use "must" "have (got) to" "ought to" "should" 1. If you

If you want to be fit, you should not eat cake, but you certainly have to walk a lot.

If you want to be fit, you shouldnt eat cake, but you certainly have to walk a lot.

Explain: When you must do something, you have to do it. It is used for a situation that has no choice. Have to is used for obligations.

If you want to be fit, you should not eat cake, but you certainly ought to walk a lot.

Explain: When we should do something, but we do not have to do if, we ought to do it. It is not as strong as must. Ought to is not usually used in questions or negative sentences. Use it to advise or make recommendations.