Helping and Modal Auxiliary Verbs

    Helping verbs or auxiliary verbs such as will, shall, may, might, can, could, must, ought to, should, would, used to, need are used in conjunction with main verbs to express shades of time and mood. The combination of helping verbs with main verbs creates what are called verb phrases or verb strings. In the following sentence, "will have been" are helping or auxiliary verbs and "studying" is the main verb; the whole verb string is underlined:

• As of next August, I will have been studying chemistry for ten years.

            Students should remember that adverbs and contracted forms are not, technically, part of the verb. In the sentence, "He has already started." the adverb already modifies the verb, but it is not really part of the verb. The same is true of the 'nt in "He hasn't started yet" (the adverb not, represented by the contracted n't, is not part of the verb, has started).

            Shall, will and forms of have, do and be combine with main verbs to indicate time and voice. As auxiliaries, the verbs be, have and do can change form to indicate changes in subject and time.

• I shall go now.
• He had won the election.
• They did write that novel together.
• I am going now.
• He was winning the election.
• They have been writing that novel for a long time.

Uses of Shall and Will and Should

            In England, shall is used to express the simple future for first person I and we, as in "Shall we meet by the river?" Will would be used in the simple future for all other persons. Using will in the first person would express determination on the part of the speaker, as in "We will finish this project by tonight, by golly!" Using shall in second and third persons would indicate some kind of promise about the subject, as in "This shall be revealed to you in good time." This usage is certainly acceptable in the U.S., although shall is used far less frequently. The distinction between the two is often obscured by the contraction 'll, which is the same for both verbs.

            In the United States, we seldom use shall for anything other than polite questions (suggesting an element of permission) in the first-person:

• "Shall we go now?"
• "Shall I call a doctor for you?"

            (In the second sentence, many writers would use should instead, although should is somewhat more tentative than shall.) In the U.S., to express the future tense, the verb will is used in all other cases.

            Shall is often used in formal situations (legal or legalistic documents, minutes to meetings, etc.) to express obligation, even with third-person and second-person constructions:

• The board of directors shall be responsible for payment to stockholders.
• The college president shall report financial shortfalls to the executive director each semester."

            Should is usually replaced, nowadays, by would. It is still used, however, to mean "ought to" as in

• You really shouldn't do that.
• If you think that was amazing, you should have seen it last night.

            In British English and very formal American English, one is apt to hear or read should with the first-person pronouns in expressions of liking such as "I should prefer iced tea" and in tentative expressions of opinion such as

• I should imagine they'll vote Conservative.
• I should have thought so.

Uses of Do, Does and Did

            In the simple present tense, do will function as an auxiliary to express the negative and to ask questions. (Does, however, is substituted for third-person, singular subjects in the present tense. The past tense did works with all persons, singular and plural.)

• I don't study at night.
• She doesn't work here anymore.
• Do you attend this school?
• Does he work here?

            These verbs also work as "short answers," with the main verb omitted.

• Does she work here? No, she doesn't work here.

            With "yes-no" questions, the form of do goes in front of the subject and the main verb comes after the subject:

• Did your grandmother know Truman?
• Do wildflowers grow in your back yard?

            Forms of do are useful in expressing similarity and differences in conjunction with so and neither.

• My wife hates spinach and so does my son.
• My wife doesn't like spinach; neither do I.

            Do is also helpful because it means you don't have to repeat the verb:

• Larry excelled in language studies; so did his brother.
• Raoul studies as hard as his sister does.

            The so-called emphatic do has many uses in English.

1. To add emphasis to an entire sentence: "He does like spinach. He really does!"
2. To add emphasis to an imperative: "Do come in." (actually softens the command)
3. To add emphasis to a frequency adverb: "He never did understand his father." "She always does manage to hurt her mother's feelings."
4. To contradict a negative statement: "You didn't do your homework, did you?" "Oh, but I did finish it."
5. To ask a clarifying question about a previous negative statement: "Ridwell didn't take the tools." "Then who did take the tools?"
6. To indicate a strong concession: "Although the Clintons denied any wrong-doing, they did return some of the gifts."

            In the absence of other modal auxiliaries, a form of do is used in question and negative constructions known as the get passive:

• Did Rinaldo get selected by the committee?
• The audience didn't get riled up by the politician.

 

Uses of Have, Has and Had

            Forms of the verb to have are used to create tenses known as the present perfect and past perfect. The perfect tenses indicate that something has happened in the past; the present perfect indicating that something happened and might be continuing to happen, the past perfect indicating that something happened prior to something else happening. (That sounds worse than it really is!) See the section on Verb Tenses in the Active Voice for further explanation; also review material in the Directory of English Tenses.

            To have is also in combination with other modal verbs to express probability and possibility in the past.

• As an affirmative statement, to have can express how certain you are that something happened (when combined with an appropriate modal + have + a past participle): "Georgia must have left already." "Clinton might have known about the gifts." "They may have voted already."
• As a negative statement, a modal is combined with not + have + a past participle to express how certain you are that something did not happen: "Clinton might not have known about the gifts." "I may not have been there at the time of the crime."
• To ask about possibility or probability in the past, a modal is combined with the subject + have + past participle: "Could Clinton have known about the gifts?"
• For short answers, a modal is combined with have: "Did Clinton know about this?" "I don't know. He may have." "The evidence is pretty positive. He must have."

            To have (sometimes combined with to get) is used to express a logical inference:

• It's been raining all week; the basement has to be flooded by now.
• He hit his head on the doorway. He has got to be over seven feet tall!

            Have is often combined with an infinitive to form an auxiliary whose meaning is similar to "must."

• I have to have a car like that!
• She has to pay her own tuition at college.
• He has to have been the first student to try that.

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.

            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 onConditional 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.

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 to 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.

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.

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.

Source : http://grammar.ccc.commnet.edu/grammar/auxiliary.htm