Grammar Rules for Modal Verbs

Modal verbs don't work the same way main verbs do. Here are some of the grammatical features that make them special:

1. Modal verbs don't add -s to third person singular forms.

It might start at 7 PM.
He can ride a bicycle.

2. In all tenses, even simple present and simple past, you use not to form the negative (rather than do + not)

She would not forget her daughter's birthday.
We could not miss the party!

3. Questions are formed through inversion.

We would read the newspaper everyday if we had a subscription.
becomes
Would we read the newspaper everyday if we had a subscription?

4. Typically, modal verbs don't conform to tense rules like other verbs. They don't change to show future or past tense

They had to practice long hours.
Incorrect Example:*They musted practice long hours.*

The students will be able to speak Spanish.
Incorrect example: *The students will can speak Spanish.*

5. Lastly, and most characteristically, modal verbs are followed by the bare infinitive of the main verb - the form without "to."

You could eat dinner earlier.