What Is the Definition of a Modal Verb in English?

modal verbs
The core modals in English. sorendls/Getty Images

In English grammar, a modal is a verb that combines with another verb to indicate mood or tense. A modal (also known as a modal auxiliary or modal verb) expresses necessity, uncertainty, ability, or permission. To put it another way, modals are how we describe our worldview and articulate our perspective.

Modal Basics

Don't feel bad if you're struggling to learn how modal verbs function in English. Even advanced students struggle with all the finer points of using these irregular verbs. Most linguists agree that there are 10 core or "pure" modals in English:

  • Can
  • Could
  • May
  • Might
  • Must
  • Ought
  • Shall
  • Should
  • Will
  • Would

Other verbs—including need, had better, and invariant be—may also function as modals (or semimodals). Unlike other auxiliaries, models have no -s, -ing, -en, or infinitive forms. (Because ought requires a to- infinitive complement, some linguists regard it as a marginal modal.)


There are two kinds of modal verbs: pure modals and semimodals. Pure modals never change their form, regardless of subject, and they don't change to show past tense. These verbs express certainty. For example: ​

  • I can sing. Bob can sing. They can sing.
  • I had to sing. She had to sing. We had to sing.

Semimodals are used to imply a range of possibility or obligation. These verbs need to be conjugated, based on subject and tense. For example:

  • I have to take responsibility for my actions. She has to take responsibility for her actions.
  • I don't need to take responsibility for my actions. He doesn't need to take responsibility for my actions.

Usage and Examples

Modals are commonly used to express your degree of certainty about the outcome of an action. Consider these two examples:

  • Kim is his sister. He told me so.
  • Kim must be his sister because they look just like each other.

In the first example, the speaker is making a statement as if it were a matter of fact. In the second example, the statement implies a degree of uncertainty, though not enough for the speaker to doubt its truthfulness. Both sentences convey a range of possibility.

The same modal verb can be used to express different degrees of certainty or obligation, which makes mastering modals tricky. For example, consider the modal verb should go and how it's used in the following two sentences:

  • The bank closes in 15 minutes. We should go there now.
  • You should go to the bank only if you need to get cash.

In the first instance, the modal is expressing a strong degree of obligation. The speaker knows she needs to go to the bank if she wants to get there before it's too late. But in the second example, the speaker is offering a suggestion and a weak one at that. The speaker doesn't know whether his friend needs cash, so he can only offer a conditional opinion.

As you become more proficient in English, you'll discover just how frequently models are used. Here are some examples:

  • "When I was younger I could remember anything, whether it happened or not."
    (Mark Twain)
  • "She thought, I must hurry before the robbers come."
    (Jean Stafford, "The Interior Castle," 1947)
  • "[G]overnment of the people, by the people, for the people, shall not perish from the earth."
    (Abraham Lincoln, The Gettysburg Address, 1863)