MODALS IN THE PAST FORM

Modals in the past are :

1) Could.
Could is used to express possibility or past ability as well as to make suggestions and requests. "Could" is also commonly used in conditional sentences as the conditional form of "can."


Examples:

• Extreme rain could cause the river to flood the city. possibility
• Nancy could ski like a pro by the age of 11. past ability
• You could see a movie or go out to dinner. suggestion
• Could I use your computer to email my boss? request
• We could go on the trip if I didn't have to work this weekend. conditional

2) Might 

Might is most commonly used to express possibility. It is also often used in conditional sentences. English speakers can also use "might" to make suggestions or requests, although this is less common in American English.

Examples:

• Your purse might be in the living room. possibility 
• If I didn't have to work, I might go with you. conditional 
• You might visit the botanical gardens during your visit. suggestion   
• Might I borrow your pen? request

3) Would.

Would is most commonly used to create conditional verb forms. It also serves as the past form of the modal verb "will." Additionally, "would" can indicate repetition in the past. For more information on the grammar behind the modal verb "would," visit the following tutorials:Conditional Tutorial, Future in the Past, and Would Always.

Examples:

• If he were an actor, he would be in adventure movies. conditional 
• I knew that she would be very successful in her career. past of "will" 
• When they first met, they would always have picnics on the beach. repetition

4) Should.

Should is most commonly used to make recommendations or give advice. It can also be used to express obligation as well as expectation.

Examples:

·       When you go to Berlin, you should visit the palaces in Potsdam. recommendation

·       You should focus more on your family and less on work. advice

·       I really should be in the office by 7:00 AM. obligation

·       By now, they should already be in Dubai. expectation

The formula of Modals in the past form :
A.COULD + VERB BASE.

>To offer Suggestion or Possibilities.
Example :
Cika : “I’m having trouble with math.”
Riko : “Why you don’t ask Kiki? Perhaps she could help you.”

>To indicate that ability existed in the past but doesn’t exist now.
Example :
Santi : “Nik, can you climb the mango tree?”
Niko : “Well, I could climb the mango tree when I was so young, but I think I’m too heavy to climb it.”

B. WOULD + VERB BASE.
>For an action that was repeated regulary in the past.
Example :
Ani : “What did you do on holidays?”
Risma : “I would visit my grandparents and my other family in the village, but how not anymore.”

>Insert rather into the pattern and use this expression to express preferences.
Example :
Jerry : “What would you rather do in weekend, go to the party or stay at home?”
Lita : “I would rather stay at home than go to the party.”

>To express polite request.
Example :
Mr. Willy : “Would you mind posting the letter?
Reva : “No, not at all.”

C.SHOULD + VERB BASE.
>To give definite advice.
Example :
Mother : “Neva, you should study tonight. You will have math test tomorrow, won’t you?”
Neva : “I will, Mom.

D.MIGHT + VERB BASE.
Ø To tell possibilities
Example :
Dina : “Why is Riko taking the bus to get home?”
Rita : “He might get a flat time.”

Ø To express polite request.
Example :
Dimas : “Might I borrow your book?”

Vera : “Yes, of course.”

MODALS IN THE PAST 

could	permission e.g. When I was a teenager, I could go out as late as I wanted.
	general ability e.g. Tom could walk by the age of 8 months.

could have	possibility, but did not happen e.g. I could have passed my driving test if I'd really tried.
	uncertainty e.g. I guess it could have been Sandra on the phone.

    

couldn'ta	permission e.g. When I was a teenager, I couldn't stay out as late as I wanted.
	general ability e.g. I couldn't walk until I was 2.
	ability in a particular situation e.g. I tried hard but I couldn't persuade him to go to the party with us.

couldn't have	possibility/ability e.g. I couldn't possibly have passed my driving test, even if I'd tried harder.
	uncertainty e.g. It couldn't have been Sandra on the phone, could it?
	with comparative adjectives e.g. I couldn't have asked for better weather on my wedding day.
	unwillingness e.g. I couldn't have left the dog in the car for long (so I didn't).

might have	possibility (didn't happen) e.g. You might have been killed!
	uncertainty e.g. I guess I might have been a bit hard on her when she came home an hour late.
	annoyance at someone's failure to do something e.g. You might have told me that you had invited all your colleagues round for dinner!
	might have known + would (idiom to ironically express that somebody's action was typical) e.g. I might have known that he would finish with me as soon as he found out I wasn't wealthy!

might not have

uncertainty e.g. He may not have found out yet that he has passed the test.

should have	expectation Why is she late?  She should have arrived by now!
	should have + verbs of thinking e.g. I should have thought you knew.
	with be and adjectives, describing chance e.g. It was weird that you should have been staying in the same hostel last month.
	criticism (you didn't do something, but it would have been the right thing to do) e.g.  The party was such fun last night!  You should have come!