Modal verbs are special verbs which behave very differently from normal verbs. Here are some important differences:
1. Modal verbs do not take "-s" in the third person.
Examples:
Julie can speak French.
The team should be here by 6 am tomorrow.
2. You use "not" to make modal verbs negative, even in Simple Present and Simple Past.
Examples:
We should not eat junk food.
She might not come to college.
3. Many modal verbs cannot be used in the past tenses or the future tenses.
Examples:
She will can run fast. Not Correct
Naresh musted study very hard. Not Correct
Common Modal Verbs
Can
Could
May
Might
Must/Ought to
Shall
Should
Will
Would