Answer:
Modal verb is a type of verb that is used to indicates modality that is like: politeness, suggestion, order , capacity,ability , request or advice.
Modal verb always accompany the base ( infinitive) the form of another verb having sementic content.
Be careful choosing between the modal verb ' should ' and the word ' ought ' because they have the same meaning but different grammar . Ought is followed by to-infinitive. Example :
1. You ought to know that by now.
2. They ought to have insisted on some compensation.
