1
It expresses ideas such as duty and moral obligation
2
Are special and auxiliary verbs. They give additional information about the function of the main verb
3
Is used to give advices or suggestions
4
Is the past of the modal verb can
5
We often use it, to say that something is obligatory
6
We use it to talk about obligation
7
Is commonly used to express possibility , it also make request
8
Is used to talk about abilities, also to ask permission in an informal way
9
Is used to talk about possibility or permission, is used in a formal way
