MODAL AUXILIARY

Modal Auxiliaries

Other helping verbs, called modal auxiliaries or modals, such as can, could, may, might, must, ought to, shall, should, will, and would, do not change form for different subjects. For instance, try substituting any of these modal auxiliaries for can with any of the subjects listed below.
I
you (singular)
he
we
you (plural)
they can write well.

There is also a separate section on the Modal Auxiliaries, which divides these verbs into their various meanings of necessity, advice, ability, expectation, permission, possibility, etc., and provides sample sentences in various tenses. See the section on Conditional Verb Forms for help with the modal auxiliary would. The shades of meaning among modal auxiliaries are multifarious and complex. Most English-as-a-Second-Language textbooks will contain at least one chapter on their usage. For more advanced students, A University Grammar of English, by Randolph Quirk and Sidney Greenbaum, contains an excellent, extensive analysis of modal auxiliaries.
The analysis of Modal Auxiliaries is based on a similar analysis in The Scott, Foresman Handbook for Writers by Maxine Hairston and John J. Ruszkiewicz. 4th ed. HarperCollins: New York. 1996. The description of helping verbs on this page is based on The Little, Brown Handbook by H. Ramsay Fowler and Jane E. Aaron, & Kay Limburg. 6th ed. HarperCollins: New York. 1995. By permission of Addison-Wesley Educational Publishers Inc. Examples in all cases are our own.
Uses of Can and Could
The modal auxiliary can is used
• to express ability (in the sense of being able to do something or knowing how to do something):
He can speak Spanish but he can't write it very well.
• to expression permission (in the sense of being allowed or permitted do something):
Can I talk to my friends in the library waiting room? (Note that can is less formal than may. Also, some writers will object to the use of can in this context.)
• to express theoretical possibility:
American automobile makers can make better cars if they think there's a profit in it.
The modal auxiliary could is used
• to express an ability in the past:
I could always beat you at tennis when we were kids.
• to express past or future permission:
Could I bury my cat in your back yard?
• to express present possibility:
We could always spend the afternoon just sitting around talking.
• to express possibility or ability in contingent circumstances:
If he studied harder, he could pass this course.
In expressing ability, can and could frequently also imply willingness: Can you help me with my homework? Can versus May
Whether the auxiliary verb can can be used to express permission or not — "Can I leave the room now?" ["I don't know if you can, but you may."] — depends on the level of formality of your text or situation. As Theodore Bernstein puts it in The Careful Writer, "a writer who is attentive to the proprieties will preserve the traditional distinction: can for ability or power to do something, may for permission to do it.
The question is at what level can you safely ignore the "proprieties." Merriam-Webster's Dictionary, tenth edition, says the battle is over and can can be used in virtually any situation to express or ask for permission. Most authorities, however, recommend a stricter adherence to the distinction, at least in formal situations.
Authority: The Careful Writer by Theodore Bernstein. The Free Press: New York. 1998. p. 87.

Uses of May and Might
Two of the more troublesome modal auxiliaries are may and might. When used in the context of granting or seeking permission, might is the past tense of may. Might is considerably more tentative than may.
• May I leave class early?
• If I've finished all my work and I'm really quiet, might I leave early?
In the context of expressing possibility, may and might are interchangeable present and future forms and might + have + past participle is the past form:
• She might be my advisor next semester.
• She may be my advisor next semester.
• She might have advised me not to take biology.
Avoid confusing the sense of possibility in may with the implication of might, that a hypothetical situation has not in fact occurred. For instance, let's say there's been a helicopter crash at the airport. In his initial report, before all the facts are gathered, a newscaster could say that the pilot "may have been injured." After we discover that the pilot is in fact all right, the newscaster can now say that the pilot "might have been injured" because it is a hypothetical situation that has not occurred. Another example: a body had been identified after much work by a detective. It was reported that "without this painstaking work, the body may have remained unidentified." Since the body was, in fact, identified, might is clearly called for.
Uses of Will and Would
In certain contexts, will and would are virtually interchangeable, but there are differences. Notice that the contracted form 'll is very frequently used for will.
Will can be used to express willingness:
• I'll wash the dishes if you dry.
• We're going to the movies. Will you join us?
It can also express intention (especially in the first person):
I'll do my exercises later on and prediction:
• specific: The meeting will be over soon.
• timeless: Humidity will ruin my hairdo.
• habitual: The river will overflow its banks every spring.
Would can also be used to express willingness:
• Would you please take off your hat?
It can also express insistence (rather rare, and with a strong stress on the word "would"):
• Now you've ruined everything. You would act that way.
and characteristic activity:
• customary: After work, he would walk to his home in West Hartford.
• typical (casual): She would cause the whole family to be late, every time.
In a main clause, would can express a hypothetical meaning:
• My cocker spaniel would weigh a ton if I let her eat what she wants.
Finally, would can express a sense of probability:
I hear a whistle. That would be the five o'clock train

Uses of Used to
The auxiliary verb construction used to is used to express an action that took place in the past, perhaps customarily, but now that action no longer customarily takes place:
• We used to take long vacation trips with the whole family.
The spelling of this verb is a problem for some people because the "-ed" ending quite naturally disappears in speaking: "We yoostoo take long trips." But it ought not to disappear in writing. There are exceptions, though. When the auxiliary is combined with another auxiliary, did, the past tense is carried by the new auxiliary and the "-ed" ending is dropped. This will often happen in the interrogative:
• Didn't you use to go jogging every morning before breakfast?
• It didn't use to be that way.
Used to can also be used to convey the sense of being accustomed to or familiar with something:
• The tire factory down the road really stinks, but we're used to it by now.
• I like these old sneakers; I'm used to them.
Used to is best reserved for colloquial usage; it has no place in formal or academic text.

Function

Modal auxiliary verbs give more information about the function of the main verb that follows it. Although having a great variety of communicative functions, these functions can all be related to a scale ranging from possibility ("can") to necessity ("must"). Within this scale there are two functional divisions:
• one concerned with possibility and necessity in terms of freedom to act (including ability, permission and duty),
• and the other ("shall" not included) concerns itself with the theoretical possibility of propositions being true or not true, including likelihood and certainty.
Most modal auxiliary verbs have two distinct interpretations, epistemic (expressing how certain the factual status of the embedded proposition is) and deontic (involving notions of permission and obligation). The following sentences illustrate the two uses of must:
• epistemic: You must be starving. (= "It is necessarily the case that you are starving.")
• deontic: You must leave now. (= "You are required to leave now.")
• ambiguous: You must speak Spanish.
o epistemic = "It is surely the case that you speak Spanish (e.g., after having lived in Spain for ten years)."
o deontic = "It is a requirement that you speak Spanish (e.g., if you want to get a job in Spain)."
Epistemic modals can be analyzed as raising verbs, while deontic modals can be analyzed as control verbs.
Another form of modal auxiliary is the verb indicating ability: "can" in English, "können" in German, and "possum" in Latin. For example, "I can say that in English," "Ich kann das auf Deutsch sagen," and "Illud Latine dicere possum."
Sometimes, the use of the modal auxiliary verbs varies in positive and negative statements. For example, in English, we have the sentence pair, "You may do that," and "You may not do that." However, in German, these ideas are expressed as "Sie dürfen das tun," but "Sie müssen das nicht tun." The latter looks as if it would translate into English as "You must not do that," but it is more typically translated as "You may not do that."
List

This table lists some modal verbs with common roots in English, German and Dutch. English modal auxiliary verb provides an exhaustive list of modal verbs in English.
Words in the same row share the same etymological root. Because of semantic drift, however, words in the same row may no longer be proper translations of each other. In addition, the English and German verbs will are completely different in meaning, and the German one has nothing to do with constructing the future tense. These words are false friends.
In English, the plural and singular forms are identical. For German and Dutch, both the plural and singular form of the verb are shown.
Note that the words in this list are not translations of each other. (See above.)
English German Dutch
can können, kann kunnen, kan
shall sollen, soll zullen, zal
will wollen, will willen, wil
must müssen, muss moeten, moet
may mögen, mag mogen, mag
tharf[1]
dürfen, darf durven, durf
The English could is the past tense of can; should is the past tense of shall; and might is the past tense of may. (This is ignoring the use of "may" as a vestige of the subjunctive mood in English.) These verbs have acquired an independent, present tense meaning. The German verb möchten is sometimes taught as a vocabulary word and included in the list of modal verbs, but it is actually the past subjunctive form of mögen. An example of the subjective use of "may" in English is in the sentence "That may be, or may not be," meaning "That could be true, but maybe it is not."
The English verbs dare and need have both a modal use (he dare not do it), and a non-modal use (he doesn't dare to do it). The Dutch verb durven is not considered a modal (but it is there, nevertheless) because its modal use has disappeared, but it has a non-modal use analogous with the English dare. Other English modal verbs include want, wish, hope, and like. All of these differ from the main modals in English (i.e. most of those in the table above) in that they take the particle to in the infinitive, like all other English verbs (may; to want), and are followed by to when they are used as a modal (may go; want to go). Some may be more than one word, such as "had better" and "would rather."
Morphology and syntax
Germanic modal verbs are preterite-present verbs, which means that their present tense has the form of a vocalic preterite. This is the source of the vowel alternation between singular and plural in German and Dutch. Because of their preterite origins, modal verbs also lack the suffix (-s in modern English, -t in German and Dutch) that would normally mark the third person singular form:
normal verb modal verb
English he works he can
German er arbeitet er kann
Dutch hij werkt hij kan
The main verb that is modified by the modal verb is in the infinitive form and is not preceded by the word to (German: zu, Dutch: te). There are verbs that may seem somewhat similar in meaning to modal verbs (e.g. like, want), but the construction with such verbs would be different:
normal verb modal verb
English he tries to work he can work
German er versucht zu arbeiten er kann arbeiten
Dutch hij probeert te werken hij kan werken
In English, main verbs but not modal verbs always require the auxiliary verb do to form negations and questions, and can be used to form emphatic affirmative statements. Neither negations nor questions in early modern English used to require do.
normal verb modal verb
affirmative he works he can work
negation he does not work he cannot work
emphatic he does work hard he can work hard
question does he work here? can he work at all?
negation + question does he not work here? can he not work at all?
(German never uses "do" as an auxiliary verb for any function; Dutch uses "do" as an auxiliary, but only in colloquial speech)
In English, modal verbs are called defective verbs because of their incomplete conjugation: they have a narrower range of functions than ordinary verbs. For example, most have no infinitive or gerund.