English verbs ~ Modal verbs
Modal verbs, also called modal auxiliaries or simply modals, are a type of auxiliary verb or helping verb. English has ten modal verbs:
Modals express the mood a verb, such as ability, possibility, necessity, or another condition. They are used with a main verb to form a sentence or a question. Modals are not conjugated, have no tense, and cannot be used without a main verb.
When used with modal verbs (except ought), main verbs always remain in the infinitive without to.
In a statement the word order is subject + modal + main verb.
In questions, the word order changes to modal + subject + main verb.
The modal can indicates possibility or ability:
Tom can help you.
In questions, the modal can requests permission to do something or to ask about possibilities:
Can I help you?
Could indicates possibility or ability in the past:
I could have told you that.
Could speculates about future posibilities. In the following examples could and might are synonomous.
In yes-no questions, could speculates about present posibilities:
Could she be the murderer?
It can also make a request. In these examples could and can are synonomous, but could is more polite.
Could / Can you open your window?
Could indicates an option:
We could go see a movie.
The modal could is also used to form the conditional. The conditional contains an if clause and a result clause. Could is placed in the result clause.
In these examples, could expresses hypothetical situations:
If I had time, I could play tennis with you.
Could mentions something that didn't happen because a certain condition was not met:
If we had left sooner, we could have taken the train.
The modals shall/will + main verb are used to create future tenses. These modals indicate an intention or an action that is expected to happen in the future.
When used in statements, there is no difference in meaning between these two modals; however, shall is rarely used in American English.
I will / shall close the door for you.
In wh- questions, shall and will ask about options.
Who will / shall drive the car?
In yes-no questions, shall and will have different meanings.
Will asks a favor.
Will also asks for information or knowledge about somebody or something.
Shall asks about a preference. In these examples, shall and should are synonomous. In American English, shall is rarely used; when it is, it's only in the first person singular and plural.
Should / Shall I close the door?
I may / might go to the park, or I may / might stay home.
iMay or can gives instructions or permission.
You may / can now board the airplane.
In yes-no questions that make a request, you can use may or can. May is more polite.
You can might in place of may or can, but this is extremely rare in American English.
May / Can / Might I be of some assistance?
You must see this movie.
Must also indicates an assumption or probability.
My watch must be broken.
In wh- questions, must is an obligation and can be replaced with the modal should. In American English, should is much more common in these types of questions.
When should / must we be there?
Must can sometimes form rhetorical questions, when you want the person to stop doing something.
The modals should and ought to indicate an obligation. These two modals are synonymous.
You should / ought to call your mother.
When used in questions, should asks if an obligation exists. Ought is never used in questions in American English.
Should he call her?
Would followed by like is a polite way of stating a preference.
I would like white wine with my fish.
In questions, would + subject + like is a polite request for a choice to be made.
Would you like soup or salad with your meal?
Would can make a request sound more polite.
Would explains an action as a result of a supposed or real condition.
I would go with you if I didn't have to work.
Would introduces habitual actions in the past.
When I was a student, I would go swimming every day.
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