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What Are Modal Verbs?

Updated on April 27, 2023Grammar

Modal verbs show possibility, intent, ability, or necessity. Because they’re a type of auxiliary verb (helper verb), they’re used alongside the infinitive form of the main verb of a sentence. Common examples of modal verbs include can, should, and must.

Modal verbs can be tricky, but the good news is that they’re simple once you learn how they work. Below, we explain everything you need to know to use modal verbs with ease.

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How are modal verbs used?

Modal verbs are used to express certain hypothetical conditions, such as advisability, capability, or requests (there’s a full list in the next section). They’re used alongside a main verb to inflect its meaning.

Consider the difference between these two examples:

I swim every Tuesday.

I can swim every Tuesday.

The first example is a simple factual statement. The speaker participates in a swimming activity every week on Tuesdays.

The second example uses the modal verb can. Notice how the meaning changes slightly. The speaker does not necessarily swim every Tuesday; they’re saying that they are capable of swimming every Tuesday or that the possibility exists for them to swim every Tuesday. It’s hypothetical.

Because modal verbs are auxiliary, they can’t generally be used on their own. A modal verb can appear alone only in a sentence only if the main verb is implied because it has previously been established.

Can you swim every Tuesday?

Yes, I can.

Modal verbs are quite common in English; you’ve seen them in action hundreds of times even if you didn’t know what they were called. The most frequently used ones are:

  • can
  • may
  • might
  • could
  • should
  • would
  • will
  • must

There are other, less common modal verbs. Some—like shall and ought—are rarely used any longer. There are also verbs that can function either as main verbs or as modal auxiliaries depending on the context; got, need, and have all behave like modal verbs in the common colloquial expressions got to, need to, and have to. Some modal verbs express very specific conditions that don’t come up often, like dare in its modal form in “Dare I ask?” The word used in the idiomatic phrase used to, as in “I used to be an English student too,” behaves like a modal verb with only a past tense form.

When are modal verbs used?

What special conditions do modal verbs indicate? Here’s a list, along with examples:

Likelihood

Some things seem likely to be true but can’t be stated as definite facts. In these cases, you can use the modal verbs should and must to show probability without certainty.

Her parents must be so proud.

My baby brother should be asleep by now.

Possibility

In a situation when something is possible but not certain, use the modal verb could, may, or might.

Judging by the clouds, it might rain today.

She may become the youngest pro soccer player ever.

Ability

The modal verb can expresses whether the subject of a sentence is able to do something. Likewise, the negative form, cannot or can’t, shows that the subject is unable to do something.

She can speak three languages but none of them well.

You can lead a horse to water, but you can’t make it drink.

Permission

If you want to ask permission to do something, start your question with can, may, or could. Traditionally, may is considered more formal and polite usage for permission; if you ask “Can I go to the bathroom?” it could be misinterpreted as “Do I have the ability to go to the bathroom?” However, in modern informal usage, may and can are both perfectly acceptable options for describing possibility or permission.

Students, you may leave early today.

Could I play too?

Request

Similarly, if you want to ask someone else to do something, start your question with will, would, can, or could.

Would you get that box off the top shelf?

Will you turn that music down?

Suggestion/advice

What if you want to recommend a course of action but not command it? If you’re giving suggestions or advice without ordering someone around, you can use the modal verb should.

You should try the lasagna.

That guy should wear less cologne.

Command

On the other hand, if you want to command someone, use the modal verbs must, have, or need. With the latter two, the main verb does not drop the word to from its infinitive form.

You must wash your hands before cooking.

You need to be here before 8:00.

Obligation or necessity

Modal verbs can express a necessary action, such as an obligation, duty, or requirement. Likewise, the negative forms express that an action is not necessary. Use the same modal verbs as with commands: must, have, and need.

We have to wait for our boss to arrive before we open.

You don’t need to come if you don’t want to.

Habit

To show an ongoing or habitual action—something the subject does regularly—you can use the modal verb would for the past tense and will for the present and future. The phrase used to is also acceptable when you’re talking about a habit in the past.

When I lived alone, I would fall asleep with music.

I will arrive early to every meeting and leave late.

How to use modal verbs (with examples)

Luckily, using modal verbs in a sentence is pretty simple. For basic sentences—in the simple present tense—just remember these rules:

  • Modal verbs come directly before the main verb except for in questions.
  • With modal verbs, use the infinitive form of the main verb. With most but not all modal verbs, to is dropped from the infinitive.

So if you want to brag about your ability to eat an entire pizza, you use the modal verb can before the infinitive form of eat without to—which is simply eat. The rest of the sentence continues as normal.

I can eat an entire pizza.

If you want to communicate that circumstances are requiring you to eat an entire pizza, you might use the modal verb have before the infinitive form of eat, retaining to:

I have to eat an entire pizza.

For yes/no questions, you still use the infinitive form of the main verb, but the order is a little different: [modal verb] + [subject] + [main verb infinitive].

Can you eat an entire pizza?

Do you have to eat an entire pizza?

Note that in the second example above, because have is a verb that only sometimes functions as an auxiliary verb and at other times functions as a main verb, the question is formed with the auxiliary verb do at the beginning.

Because modal verbs deal largely with general situations or hypotheticals that haven’t actually happened, all of the core ones can refer to present and future time but only some of them can refer to past time, and most of the time they do not change form to make different tenses. However, all of them can be used with different conjugations of a sentence’s main verb to refer to present or future time in different ways, so let’s talk a little about verb tenses and modal verbs.

Present tenses

We already covered the simple present above, but you can also use modal verbs in the present continuous and present perfect continuous tenses.

Present continuous

After the modal verb, use the word be followed by the –ing form of the main verb: [modal verb] + be + [verb in -ing form].

I should be going.

Present perfect continuous

You can add a modal verb before a main verb in the present perfect continuous tense without changing much. However, note that the main verb always forms the present perfect continuous using have been, when appearing with a modal verb, never had been, even if the subject is third-person. The formula is [modal verb] + have been + [main verb in -ing form].

She must have been sleeping.

Simple past and present perfect tenses

Using a modal verb in the simple past or the present perfect (which indicates an action that happened in the past but is directly related to the present) is a little trickier.

Only a few of the core modal verbs have the ability to refer to past time: could, might, should, and would. They do this by functioning at times as the past tense forms of their fellow modal verbs can, may, shall, and will. But keep in mind that, as we saw above, could, might, should, and would also have different senses in which they refer to the present and the future, indicating possibility, permission, request, habit, or other conditions. None of the modal verbs can be used in the past perfect, the past continuous, or the past perfect continuous tense.

Simple past

Of the main modal verbs listed at the top, only can and will can be used in the simple past. The expressions have to and need to can also be used in the simple past, when conjugated as had to and needed to. Other modal verbs use the present perfect to discuss events in the past.

Can and will use their past tense form plus the infinitive form of the main verb without to, just like in the present: could/would + [main verb infinitive].

I could do a handstand when I was a kid.

During exam season in college, I would not sleep much.

Present perfect

To form the present perfect using the modal verb could, might, should, or would, use the present perfect form of the main verb, which is have plus the past participle. As with the present perfect continuous, you always use have, even if the subject is third-person: could/might/should/would + have + [main verb past participle].

I might have gone to the party, but I forgot.

Future tenses

Because the simple future, future continuous, future perfect, and future perfect continuous tenses of main verbs are all already formed with the modal verb will, when you want to indicate likelihood, permission, or any of the other conditions discussed above in the future, it often makes sense to do it in some other way than by adding a modal verb.

They will be more likely to come over tomorrow if you give them plenty of warning.

However, there are also situations in which a modal verb other than willcan be used to talk about something in the future. In these cases, the new modal verb just replaces will in the sentence, and the main verb takes the same form it would with will..

I can hang out tomorrow.

Could I be majoring in law next year?

They should have left by the time we get there.

By twenty years from now, I may have traveled to more conferences than I care to recall.

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