Obligation Ought / should is used to express the subject’s obligation or duty.
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You should send in accurate tax returns.
Must and have to show the imprassion that the obligation is being or will be fulfilled but with ought/should we don’t
necessarily feel that the obligation is being or will be fulfilled.
If a driver says – I should drive slowly here. It’s a build-up area. He usually implies that he isn’t going to go slowly.
If he really intended to go slowly he would say – I must drive here slowly. It’s a build-up area.
Should can be used in formal notes and information sheets.
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Candidates should be prepared to answer questions by June.
In this case must can be used without change of meaning but should is more gentle or polite.
