Modals

What is modal? 

• A modal is defined as an auxiliary verb that is used with a main verb to express particular attitude to an event or a situation. 
• Modals are always used with other verbs. They are a special kind of auxiliary verb. We sometimes call them modal verbs or modal auxiliaries. 

Source

Features of modals

1. Modals do not take "-s" in the third person.

Examples:

He can speak Chinese.
She should  be here by 9:00.

2. You use "not" to make modals negative, even in simple present and simple past.

Examples:

He should not be late.

They might not come to the party.

3. Many modals cannot be used in the past tenses or the future tenses.

Examples:

He will can go with us. Incorrect

She must studied very hard. Incorrect