Modal Auxiliary Verbs  

What is a modal auxiliary verb?

A modal auxiliary verb, often simply called a modal verb or even just a modal, is used to change the meaning of other verbs (commonly known as main verbs) by expressing modality—that is, asserting (or denying) possibility, likelihood, ability, permission, obligation, or future intention.
Modal verbs are defined by their inability to conjugate for tense and the third person singular (i.e., they do not take an “-s” at the end when he, she, or it is the subject), and they cannot form infinitives, past participles, or present participles. All modal auxiliary verbs are followed by a main verb in its base form (the infinitive without to); they can never be followed by other modal verbs, lone auxiliary verbs, or nouns.
As with the primary auxiliary verbs, modal verbs can be used with not to create negative sentences, and they can all invert with the subject to create interrogative sentences.

The Modal Verbs

There are nine “true” modal auxiliary verbs: will, shall, would, should, can, could, may, might, and must. The verbs dare, need, used to, and ought to can also be used in the same way as modal verbs, but they do not share all the same characteristics; for this reason, they are referred to as semi-modal auxiliary verbs, which are discussed in a separate section.
We’ll give a brief overview of each modal verb below, but you can continue on to their individual sections to learn more about when and how they are used.

Will

As a modal auxiliary verb, will is particularly versatile, having several different functions and meanings. It is used to form future tenses, to express willingness or ability, to make requests or offers, to complete conditional sentences, to express likelihood in the immediate present, or to issue commands.

Shall

The modal auxiliary verb shall is used in many of the same ways as will: to form future tenses, to make requests or offers, to complete conditional sentences, or to issue maxims or commands. Although will is generally preferred in modern English, using shall adds an additional degree of politeness or formality to the sentence that will sometimes lacks.
Generally, shall is only used when I or we is the subject, though this is not a strict rule (and does not apply at all when issuing commands, as we’ll see).

Would

The modal auxiliary verb would has a variety of functions and uses. It is used in place of will for things that happened or began in the past, and, like shall, it is sometimes used in place of will to create more formal or polite sentences. It is also used to express requests and preferences, to describe hypothetical situations, and to politely offer or ask for advice or an opinion.

Should

The modal verb should is used to politely express obligations or duties; to ask for or issue advice, suggestions, and recommendations; to describe an expectation; to create conditional sentences; and to express surprise. There are also a number of uses that occur in British English but are not common in American English.

Can

As a modal auxiliary verb, can is most often used to express a person or thing’s ability to do something. It is also used to express or ask for permission to do something, to describe the possibility that something can happen, and to issue requests and offers.

Could

The modal verb could is most often used as a past-tense version of can, indicating what someone or something was able to do in the past; it can also be used instead of can as a more polite way of making a request or asking for permission. Could is also used to express a slight or uncertain possibility, as well as for making a suggestion or offer.

May

The modal verb may is used to request, grant, or describe permission; to politely offer to do something for someone; to express the possibility of something happening or occurring; or to express a wish or desire that something will be the case in the future. We can also use may as a rhetorical device to express or introduce an opinion or sentiment about something.

Might

The modal verb might is most often used to express an unlikely or uncertain possibility. Might also acts as a very formal and polite way to ask for permission, and it is used as the past-tense form of may when asking permission in reported speech. It can also be used to suggest an action, or to introduce two differing possibilities.

Must

The modal verb must is most often used to express necessity—i.e., that something has to happen or be the case. We also use this sense of the word to indicate a strong intention to do something in the future, to emphasize something positive that you believe someone should do, and to rhetorically introduce or emphasize an opinion or sentiment. In addition to indicating necessity, must can be used to indicate that something is certain or very likely to happen or be true.

Using Modal Verbs

Modal auxiliary verbs are used to uniquely shift the meaning of the main verb they modify, expressing things such as possibility, likelihood, ability, permission, obligation, or intention. As we will see, how and when we use modal verbs greatly affects the meaning of our writing and speech.

Subtleties in meaning

Modal verbs attach differing shades of meaning to the main verbs they modify. It is often the case that this difference in meaning is or seems to be very slight. To get a better sense of these differences in meaning, let’s look at two sets of examples that use each of the modal verbs we discussed above in the same sentence, accompanied by a brief explanation of the unique meaning each one creates.
  • “I will go to college in the fall.” (It is decided that I am going to attend college in the fall.)
  • “I shall go to college in the fall.” (A more formal way of saying “I will go to college in the fall,” possibly emphasizing one’s determination to do so.)
  • “I would go to college in the fall.” (I was planning to attend college in the fall (but something not stated is preventing or dissuading me from doing so).)
  • “I should go to college in the fall.” (It is correct, proper, or right that I attend college in the all.)
  • “I can go to college in the fall.” (I am able to attend college in the fall.)
  • “I could go to college in the fall.” (I have the ability to attend college in the fall, but it is not decided.)
  • “I may go to college in the fall.” (I will possibly attend college in the fall, but it is not decided.)
  • “I might go to college in the fall.” (I will possibly attend college in the fall, but it is not decided.)
  • “I must go to college in the fall.” (I have to attend college in the fall, but it is not decided.)
  • Will we spend the summer in Florida?” (Is it the future plan that we are going to spend the summer in Florida?)
  • Shall we spend the summer in Florida?” (A more formal way of asking “Will we spend the summer in Florida?”)
  • Would we spend the summer in Florida?” (Has the plan been made that we spend the summer in Florida?)
  • Should we spend the summer in Florida?” (Is it correct or preferable that we spend the summer in Florida?)
  • Can we spend the summer in Florida?” (Can we have permission to spend the summer in Florida? Or: Are we able to spend the summer in Florida?)
  • Could we spend the summer in Florida?” (Slightly more polite way of asking for permission to spend the summer in Florida.)
  • May we spend the summer in Florida?” (More formal or polite way of asking for permission to spend the summer in Florida.)
  • Might we spend the summer in Florida?” (Overly formal way of asking for permission to spend the summer in Florida.)
  • Must we spend the summer in Florida?” (Very formal way of asking if it is necessary or required that we spend the summer in Florida.)

Substituting Modal Verbs

As we can see from the above sets of examples, the different modal verbs often have very similar meanings, and it’s sometimes unclear when it is appropriate to use one instead of another. To explore the subtle differences in meaning that occur when we substitute certain modal verbs, go to the section on Substituting Modal Verbs.

Omitting main verbs

A modal verb must always be used with a main verb—they cannot stand completely on their own.
However, it is possible to use a modal verb on its own by omitting the main verb, so long as it is implied by the context in or around the sentence in which the modal is used. This can occur when a sentence is in response to another one, or when the clause with the modal verb occurs later in a sentence in which the main verb was already stated. For example:
  • Speaker A: “I’m thinking about taking up scuba diving.”
  • Speaker B: “I think you should!” (The verb taking up is omitted in the second sentence because it is implied by the first.)
  • “I’d like to switch my major to mathematics, but I’m not sure I can.” (The verb switch is omitted in the final clause because it appears earlier in the same sentence.)

Using adverbs

Generally speaking, we use adverbs after a modal verb and either before or after the main verb in a clause. Sometimes putting an adverb before a modal is not incorrect, but it will sound better if placed after it. For example:
However, this is not a strict rule, and certain adverbs are able to go before the modal verb without an issue. For example:
When a modal verb is made negative, though, it is sometimes the case that an adverb must go before the modal verb. For example:
Unfortunately, there is no rule that will explain exactly when one can or cannot use an adverb before a modal verb—we just have to learn the correct usage by seeing how they are used in day-to-day speech and writing.

Common errors

Mixing modal verbs

Remember, a modal verb is only used before a main verb, or sometimes before be or have when they are used to create a verb tense. We do not use a modal verb before auxiliary do, or in front of other modal verbs. For example:

Conjugating the third-person singular

When main verbs function on their own, we conjugate them to reflect the third-person singular (usually accomplished by adding “-s” to the end of the verb).
However, we do not conjugate modal verbs in this way, nor do we conjugate a main verb when it is being used with a modal.
For example:

Conjugating past tense

Similarly, we cannot use modal verbs with main verbs that are in a past-tense form; the verb that follows a modal must always be in its base form (the infinitive without the word to). Instead, we either use certain modal verbs that have past-tense meanings of their own, or auxiliary have to create a construction that has a specific past-tense meaning.
For example:

Following modal verbs with infinitives

As we saw above, all modal auxiliary verbs must be followed by the base form of the main verb. Just as we cannot use a modal verb with a main verb in its past-tense form, we also cannot use a modal verb with an infinitive:
Quiz

1. Which of the following is a not a function of a modal auxiliary verb?





2. Which of the following modal verbs indicates necessity?





3. Which of the following modal verbs is used to request permission?





4. Which of the following is something that a modal verb cannot do?





5. When can a modal verb stand on its own?






6. Which of the following is not one of the “true” modal verbs?





Chapter Sub-sections

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