Introduction

Modal verbs (can, could, must, should, ought to, had better, may, might, will, would, shall) are auxiliary verbs that express ability, necessity, request, permission, advice, desire, probability, etc. Modal verbs express the speaker's attitude to the action indicated by the main verb.

She can drive. (ability)
I must go. (strong necessity)
You should call him. (advice)
Could you help me with this report, please? (request)
You may stay here. (permission)
I would like to see her. (desire)
He might leave soon. (possibility)
He must be at the tennis club now. (strong probability)