Modals or Modal Verbs are the words that, while acting as auxiliaries, express various modes or moods of an action. Can, Could, May, Might, Shall, Should, Will, Would, Must, Ought to, Need, Dare, and Used to are Modal Verbs.
- You may sit wherever you like.
- The scorpion might have stung the boy.
- He is ill, he must consult the doctor.
- My younger brother can solve any puzzle easily.
- Children must not touch electric wires.
The highlighted words (may, might, must, can and much) in the above sentences show various moods behind their respective verbs sit, sting, consult, solve, and touch. Therefore, they are modal verbs.
Modal auxiliaries are capable of expressing various modes or moods without being limited by the tense. They remain unaffected by the changes in the number or gender of the subject or the object of the main verb.