English Grammar

Modal Auxiliary Verbs

by Eugene R. Moutoux

1. Authorities differ among themselves as to which verbs should be called modal auxiliaries. My own list includes these seven: can, could, may, might, must, should, and would. Since it is impossible to discuss the modals without reference to the indicative and the subjunctive moods, letís be sure we have a clear idea of those terms.

2. Actually, English has three moods (or modes): indicative, imperative, and subjunctive. The imperative is the easiest to grasp. It includes the verb forms used to command someone to do something: Go! Run! Sit! Speak! In each case, the imperative is the same in form as the present infinitive (to go, to run, to sit, to speak) without the particle to. This is even true of the infinitive to be, whose imperative form is be (as in Be good! or Be quiet!). Imperatives do not have to be followed by an exclamation mark, but they often are. Interestingly, modal auxiliary verbs cannot be used in the imperative mood.

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3. The indicative mood is used for pointing out, describing, or asking about actual things or happenings. Most verb forms that we use every day are indicative. Here are some sentences whose verbs are in the indicative mood: 

- It is snowing. 

- That has been my house for the last ten years. 

- When does the movie begin? I had a headache. 

- Will you be my friend?

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4. Three modal forms, can, may, and must, are always indicative. Ronald can run fast says simply that Ronald has the ability to run fast. The children may go with us says that the children have permission to accompany us or that it is possible that they will go with us. Stella must stay home this evening tells of a particular obligation incumbent upon Stella. If we want to put Ronaldís ability to run fast in the past, we can say When he was young, Ronald could run fast; however, we must choose altogether different verbs if we want to place the childrenís permission and Stellaís obligation in the past: 

- The children were permitted to go with us

- Stella had to stay home that evening.

5. The modal auxiliary verb could is used not only in the past indicative but also in the present subjunctive (see the page entitled "Subjunctive Mood"): If Ronald had not injured his foot, he could run fast. In this sentence, could does not refer to an actual ability but only to an ability Ronald would have if he had not hurt himself. This sentence rules out Ronaldís ability to run fast here and now. We have a slightly different situation in the sentence If Ronald wanted to, he could run fast. This sentence implies one of two things depending on context: it is impossible for Ronald to run fast because he doesnít want to, or it is improbable that Ronald can run fast because it is improbable that he wants to. You can swing probability to the positive side by choosing the indicative: Ronald can run fast if he wants to.

6. Might is the present subjunctive form of may. Note the difference between If she is here, she may be able to help us and If she were here, she might be able to help us. In the first sentence, her ability to help is possible (because it is possible that she is here), whereas in the second sentence the ability to help is purely speculative (because she is not here).

7. Would is used in unreal (contrary-to-fact) conditional sentences: If I had time, I would help you. Contrast that with a sentence containing a real condition: If I have time, I will help you. Interestingly, would is also used to expresses habitual action in the past, e.g., Back then people would often sit on their front porch and talk with passing neighbors.

8. Should is seldom used these days as a future-tense indicator, e.g., Next year I should like to visit my cousin in New York. It is widely used to express obligation (I really should do my homework) and expectation (You should be able to find our house).

9. Must has no subjunctive form. If we want to use the verb must in the past or as a subjunctive, we have to choose another verb: (past) They had to leave early, or (subjunctive) If he had to work harder, he would.

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10. All seven modals can be used with basic present-perfect forms (present-perfect infinitives without to). Here are some examples:

- Can and could: He cannot have finished so soon and She could have pouted but she didnít.

- May and might: If she was there, she may have been able to help them and If she had been there, she might have been able to help them. When so used, may and might retain the distinction between real and unreal, possible and impossible.

- Would: If I had had time, I would have helped you. This is an unreal conditional sentence in past time.

- Should: I really should have done my homework and You should have been able to find our house.

- Must: They must have left (not the same as They had to leave) and You must have been helped (not the same as You had to be helped).

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11. Many grammarians claim that the subjunctive mood is almost dead in English, used only in an occasional expression such as If I were you. I disagree. If I asked you for the tense of gave and lived, perhaps you would say past. And I would say you are half right. They are past indicative forms, but they are also present subjunctive forms: 

- If we gave him five dollars (right now), he would be able to eat

- If you lived closer (right now), we could get together more often.

- from the teacher's enlarged edition of my book Diagramming Step by Step: One Hundred and Fifty-one Steps to Diagramming Excellence

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