Can’t ( or couldn’t) have + past participle. :  This expression is used  to explain the opposite of ‘Must Have’ when it deals with the probability aspect. Examples will clarify the essence of this expression.

• Johny drove past me without stopping.  He can’t have seen me.( i.e probably he would not have seen me. We don’t say, he mustn’t have seen me) .   Now differentiate the expression ‘must have ‘ when used  in a positive sentence. Johny stopped his car on the way. He must have seen me walking and would have liked to offer me a lift.
•   ‘ He couldn’t have seen me. ‘ can be used in place of ‘ He can’t have seen me ‘.
• The drunkard walked straight into a wall.  He can’t have seen the wall.
• He couldn’t (or can’t) have met the minister yesterday. (maybe, the minister was very busy or otherwise engaged)

‘ Can ‘ with different degree of sharpness when used in the negative.

• We are unable to help you. ( the polite and preferred form of denial)
• We cannot help you. (more abrupt form of denial)
• We can’t help you.( the most abrupt form of denial)

Note :  ‘ We are unable to ‘ is often preferred in formal English to the more abrupt ‘ cannot’ and the still more abrupt ‘ can’t ‘.

Further (OR) Farther :  Both these are the comparative forms of ‘ Far ‘.  Further means ‘ more, additional or more distance’.  But  ‘ Farther ‘ refers only to distance.

Examples.

• We will make a decision on getting further details . ( NOT farther details.)
• It’s a long walk from here , further than I thought. ( OR farther than….)
• I can’t walk any farther. (OR any further)
• We must get further information. (NOT farther)
• We don’t want to go further into the matter.(NOT farther)
• The examination stands postponed until further notice.(NOT farther notice)

CAN :  We use ‘Can ‘ to say that something is possible or that somebody has the general ability to do something .  ‘ Can ‘ frequently precedes verbs of perception.  Thus it indicates (a) your own ability (b) positive permission (c) perception (d) possibility etc.

• Can you lift this box? (ability)
• You can drive my car.( positive permission)
• Can you hear me well?( perception)
• He can be in the town now.(possibility)
• Children can sometimes be very trying.
• It can be very cold here even in May.
• Can I borrow your pen, please?

Must :

(1)  We use ‘ Must ‘ to say that we feel /assume something.  This is to show our assumption, but when we rule out or deny the probability we should use ‘ Can’t ‘ and NOT ‘ Mustn’t ‘.( Or in other words , in negative sentences we use ‘ can’t ‘ instead of ‘ mustn’t ‘ when we deal with probability aspect)

• You’ve been travelling all day.  You must be tired.
• They have just had lunch.  They can’t be hungry.( We don’t say,  ‘they mustn’t be…)
• He must come before 8 o’ clock.( i.e based on certain assumptions, one is compelled to arrive at the conclusion that he………)
• It is 10 o’ clock  now and he is never late.  He can’t be coming.
• This must be the way, surely.
• This can’t be the way, surely.( We don’t say , ‘ This mustn’t be the way….)
• John has gone to Delhi.  He can’t be back before Friday.
• They haven’t lived here for very long.  They can’t know many people.

(2)  ‘ Must ‘ indicates obligation that is considered inescapable.( here the negative is ‘ mustn’t  ‘)

• You must look after your parents when they are old.
• You mustn’t hurt the helpless creature.
• I told him I must be very frank…..(OR) I told him I had to be……

Note:  The past equivalent of ‘ Must ‘ is  ‘ Had to ‘.  However, in the past reported speech ‘Must’ can be used in place of ‘ Had to ‘.

(3)  Must : when we want or intend to do something fairly soon.

• I must go and make a phone-call.
• I must meet him and convey this message today itself.

(4)  Must :  When we suggest that somebody should do something.

• You are a good writer.  You must publish your works.
• You must come and visit me.

Could – different usages.

(1)  ‘ Could ‘ refers to the past ability/ perception.(general or particular)

• My grandfather could speak five languages.(general)
• When we went into the house, we could smell something burning.(particular)
• I could not grasp what the old man said.(particular)

(2)  We use ‘ Could ‘ for general ability.  But, if we are talking about what happened in a particular situation, we use  ‘was/ were able to ‘.  When we use ‘ Managed to….’ , it has a special connotation that a certain amount of difficulty was involved in doing the action.

• We were able to persuade him to come for the function.(refers to a particular situation)
• Running fast, I was able to catch the bus.(refers to a particular situation)
• There was heavy rush for the show but I managed to secure a seat.(refers to a particular situation involving difficulty)

(3)  ‘ Could ‘ serves a purpose similar to that of ‘ Can ‘ , but more hesitant, less direct than ‘ Can, May, or Might ‘.

• Could this be the right answer?
• This could be the answer.  What do you think?

(4)  The negative ‘couldn’t ‘ ( could not) is possible in all situations.( i.e specific or general situations)

• I could not swim when I was a boy.
• We tried hard but we couldn’t persuade him to accept our proposal.

(5)  We also use ‘ Could ‘ to talk about possible actions for ‘Now ‘ or for a ‘ Future time’.  ‘Can’ is also possible in the place of ‘ Could ‘ ( especially to make a suggestion)

• What shall we do this evening ?
• We could go to the cinema.
• It’s a nice day.  We could go for a walk.
• (OR) We can go for a walk.
• When you go to Mumbai next month, you could stay with my uncle.  It will not be a problem for him.  He has his own flat there.

(6)  You must use ‘ Could ‘  ( Not can) when you don’t really mean what you say.

• I am so angry with him.  I could kill him.(  we do not say, ‘I can kill him’.This usage shows the intense state of anger Or it involves a little bit of exaggeration)
• I could smack his face! (here one does not smack another)
• I am so hungry.  I could eat a horse.( actually one does not eat a horse)
• I am so tired.  I could sleep for a week.( one does not ,actually, sleep for a week)

(7)  We also use ‘ Could ‘ to say that something is possible now or in the future.

• The phone is ringing.  It could be my sister Soja.
• They could arrive at any time.  Please finish all the preparations soon.

(8)  ‘ Could ‘ refers to possible freedom from other engagements.

• I could see you tomorrow at 10 a.m perhaps. ( which is less definite than ‘ I can see…)

(9)  ‘ Could ‘ for grants, permissions etc.

• Could I borrow your pen , please?
• Yes of course you could.
• (OR) I am afraid you couldn’t. ( if the answer is in the ‘Negative’)

Past Simple : (1) This tense denotes an action completed in the past as in : in 1980, in May, on Monday, at 10 a.m etc. We can mention the exact time when the action took place .

• He went to Delhi yesterday.
• They ate up all the mangoes we had kept in the basket.
• When did you see him last?
• Did he lose his key?  Yes he did.( whether he got back the key now or not is not mentioned/clear here)
• What did you say when he came to quarrel with you?
• I didn’t have any money with me to help you.
• He completed the work single-handed before schedule.

(2)  We use past tense (Not present perfect) if there is no connection with the present( for example , things that happened a long time ago)

• Chinese invented printing. (Not  ‘have invented ‘)
• How many plays did Shakespeare write? ( Not ‘ has Shakespeare written’)
• He is a historian.  He has written many books on his subject. ( He still writes books, he is still alive.  In this context, we use ‘ present perfect ‘ instead of past.)

Possessive Adjective                Possessive Pronoun

• My                                       Mine
• Your                                    Yours
• His                                      His
• Her                                      Hers
• Their                                   Theirs
• Its                                        Its
• Our                                     Ours

A Possessive Adjective in a sentence is immediately followed by a noun, but a Possessive Pronoun is not succeeded by a noun immediately.

• Is this your book? ( Possessive Adjective)
• Is this book yours? OR  Is this yours? (Possessive Pronoun)

Note: The usages of possessive adjective need not be explained as it is very clear and does not involve complicated grammatical or structural explanations.  So let’s see the usages of Possessive Pronouns.  We say ‘ a friend of mine/ yours/ hers/ ours/ theirs (NOT  ‘ a friend of me/ your/ her/ our/ their etc)

• He is an old friend of mine.(i.e one of my old friends)
• Is this yours or hers?
• He is a near relative of mine.
• He met a relation of his yesterday.
• She invited all friends of hers to her birthday party.
• A friend of yours came here yesterday.
• I met a friend of Neethu’s at the party.
• Is that boy a friend of Jithu’s?
• We went on holiday with some friends of ours.
• Mine is small house. (i.e my house is a small one)
• Yours is a beautiful one.
• Hers is a cruel mother-in-law.
• Ours is a small village.

Who…………….That : When applied to people ‘WHO’ is preferred to ‘ That’.  But after superlatives, only,  all,  any  and  ‘it is’  OR  ‘it was’  etc  ‘ THAT’ is preferred to ‘ Who ‘.

Examples for ‘ WHO ‘ preference.

• He is the boy who got the first prize.
• The man who is in charge of the library has not come.

Examples for ‘ THAT ‘ preference.

• Sachin is the best batsman that played in the last world cup. ( the best batsman – superlative)
• Dr.K.J.Yesudas is the only singer that has performed in more than fifteen thousand stages.( the only)
• Any musician that wants to sing in Guruvayoor Melpathoor Auditorium should have enough experience.( any musician)
• It is the manager that takes important decisions in our office.( it is the manager)
• All the people that were present liked the programme.( all the people)

Present Perfect Continuous : ( Structure –  Subject + has been/ have been  + verb + ing) This tense denotes an action begun some time in the past and still continuing at the time of speaking.  In this tense, we can mention the length of time involved in the action.  But, this is not possible in the case of Present Continuous Tense.

Comparison of present perfect continuous and present continuous.

• They have been studying in the government school since 2001.( This is present perfect continuous- the time involved in the action is clearly mentioned)
• They are studying in the government school.(This is present continuous – here we cannot indicate the length of time involved in the action.
• How long have you been working in the garden?
• We have been working in the garden for two hours.
• I have been reading this book since the morning.
• His hands are dirty.  He has been repairing the car.( it doesn’t matter whether the repairing has been finished or not)
• It’s nice to see you again.  What have you been doing since we last met.

Sooner or Later =  Eventually,  certainly although one cannot be sure when, at some time in future.  To explain further, you don’t  know exactly when something will happen but you are certain that it will happen.

• If you do such a mean thing, you will be punished sooner or later.
• The culprit will be brought to book sooner or later.
• You will have to tell the truth sooner or later.
• The accused has escaped from the police custody.  But he will be caught by the police sooner or later.

Could have (done):

(1) When you do not really mean what you say:

• I was so tired.  I could have slept for a week.
• When I saw the result I could have wept.( i.e I felt like weeping but I didn’t )
• I was so hungry.  I could have eaten a horse.
• He behaved so stupidly.  I was annoyed terribly.  I could have beaten him.

(2)  Most often we use ‘ Could have (done) ‘ for things which were possible but did not happen or past ability/permission unused.

• Why did you stay at a hotel when you went to Mumbai?  You could have stayed with my brother. (i.e you had the opportunity to stay with him but you didn’t)
• Did you get to the top (of the mountain)?
• We could have done, but we didn’t try.
• Why did you walk?  You could have taken my car.
• He fell of a ladder yesterday but he’s alright, he is lucky.  He could have hurt himself badly.( But fortunately, he didn’t hurt himself)
• The situation was bad but it could have been worse.

(3)  Could have (done) = would have been able to (do)

• Why didn’t you apply for the job?  You could have got it.
• We could have gone away if we had had enough money.
• She couldn’t have gone away because she was ill. (= she wouldn’t have been able to go)
• You did very well to pass the exam.  I am sure I couldn’t have been able to pass it if I had appeared for it.
• I don’t know how you worked so hard to achieve the target.  I couldn’t have done it.