Introduction:

Modals are used to change the tone of a sentence. They add elements such as possibility obligation permission etc…
Modals include: should, could, might, ought to, have to etc…

Structure:

Subject + modal + verb stem Negative Subject + modal + not + verb stem Interrogative modal + subject + stem of the verb

Examples:

Should - Use this modal to express obligation
Would - Use this modal to express possibility and condition
Could - Use this modal to express possibility
Can - Use this modal to express possibility
Have to - Use this modal to express obligation (with no choice)
Ought to - Use this modal to express obligation (with choice)
Might - Use this modal to express possibility (with choice)
Must - Use this modal to express obligation (no choice)
May - Use this modal to express to express permission and possibility.