Contents introduction chapter I grammatical meaning, grammatical form

Can not' is always written as one word,cannot'.
/ cannot go back.
However, if'can' is followed by 'not only', can' and 'not' are not joined.
We can not only book your flightfor you, but also advise you about hotels.
In spoken English and informal written English, 'not' is often shortened to '-n't' and added to the modal. The following modals are often shortened in this way:
could not- couldn 't
should not- shouldn 't
must not- mustn't
would not- wouldn 't
We couldn't leave the farm.
You mustn 't talk about Ron like that.
Note the following irregular short forms: shall not-shan't
will not-won't
cannot-can't
I shan't let you go.
Won't you change your mind?
We can't stop now.
' Might not' and ' ought not' are sometimes shortened to ' mightn't' and oughtn't'.
Note that 'may not' is very rarely shortened to 'mayn't' in modern English. To make a question, you put the modal in front of the subject.
Could you give me an example?
Will you be coming in later?


1.2 Primary and secondary functions of modal verbs.
Modals have two major functions which can be defined as primary and secondary.
In their primary function, modal verbs closely reflect the meanings often given first in most dictionaries, so that:
-can-could relate mainly to ability: I can lift 25 kg.
-may-might relate mainly to permission: you may leave early.
-will-would relate mainly to prediction: it will rain soon.
-shall after I/We relates mainly to prediction: can we find our way home?-I am sure we shall.
-must relates mainly to inescapable obligation: You must be quiet.
-needn't relates to absence of obligation: You needn't wait
The general theme in both the primary and secondary uses of modal will is the same as the theme of temporal will, namely futurity.⁵ In its primary uses, the modal will adds to the ides of futurity an expression either of volition or of confident certainty that a future event will take place, the speaker may be expressing his own volition about his own or other people's actions, or he may be attributing volition to a third party. Naturally, volition is only likely to be expressed about an action or state that is subject to human control, whether the verb is in the active voice (Someone will do that) or the passive (That will be done). We are therefore more likely to find volition expressed in an action verb than in a stative verb referring to involuntary activity.
In their secondary function, nine of the modal auxiliaries (not shall) can be used to express the degree of certainty/uncertainty a speaker feels about a possibility, they can be arranged on a scale from the greatest uncertainty (might) to the greatest certainty (must). The order of modals between might and must is not
⁵ Fowler's Dictionary of Modern English Usage (4th ed.). Oxford University Press, p. 853.
fixed absolutely. It varies according to situation. For example, one arrangement might be;⁶
You are right, (certain)
Can requires qualification to be used in this way.
He can hardly be right
Do you think he can be right?
I don't think he can be right.
We use may and might to say that something is possible. There is no important difference between them. Usually you can use may or might you can say:

• 
  It may be true. Or it might be true. (= perhaps it is true) the expressions "to be allowed and to be permitted" which have the same meaning, can be used to supply the missing forms of the verb may.
  
• 
  "May I come alone" asked Karen.
  
• 
  You are to stay in bed until you are allowed to get up.
  
• 
  "May" express permission, uncertainty, possibility, reproach.
  
• 
  May I use your phone?
  

⁶ Quirk, Randolph; Greenbaum, Sidney; Leech, Geoffrey; Svartvik, Jan (1985). A Comprehensive Grammar of the English Language. Harlow: Longman, p. 140.
- At any rate she murmured something to the effect that he might stay if he wished.
Uncertainty as to the fulfillment of an action, state or occurrence, supposition implying doubt

• 
  "You may think you are very old", he said, "but you strike me as extremely young".
  
• 
  She was and remains are a riddle to me. She may and she may not prove to be riddle to you
  

When uncertainty is expressed the time of the action is indicated by the form of the infinitive and not by the form of the modal verb, as both may and might can refer to the present ore t the past in accordance with the form of the infinitive. If the action refers to the past, the perfect infinitive is used.
Primary and secondary functions of must compared. In its primary function it requires another full verb to make up its "missing parts", (in the same way can, for example, in its primary function requires the full verb be able to make up its missing part). In its secondary function must has only two basic forms: a form which relates to the present and a for, which relates to the perfect or past.