MODALS IN THE PAST FORM

When do we use modals?

• To talk about someone's ability (or inability) to do something
  example: "We can find your house without the street plan."
  "She can't have a daughter that old!"
• To talk about an action that is necessary (or impossible, or not necessary)
  example: "You must always have your driver's licence when you are driving your car."
  "You needn't carry your passport around with you."
• To talk about a situation that is possible (or impossible)
  example: "Do be careful with that glass, the baby might knock it over"

A modal verb always has the same form:	There is no past form (-ed), no present participle (-ing) and no 3rd persons singular (-s).
Modal verbs come before the subject in questions:	example: "May I come to your house for tea?"
Negative forms:	Modal verbs have n't or not after them in the negative. example: "mustn't" - "needn't".

PRESENT FORM	PAST FORM
can	could
may	might
will	would
shall	should

Modals in the past are :
1. Could
2. Would
3. Should
4. Shall
 
Could + Verb base
We can use this expression : to offer suggestion or possibilities.

Example :
Nia : I’m having trouble with math.
Rizki : Why don’t you ask Novita ?
Perhaps she could help you.
 
Might + Verb base
Use might to tell possibillities.
Example :
Helda : Why is Rio taking the bus to get home.
Fany : He might get a flat time.

Would + verb base
Use would for an action that was repeated regulary in the past.
Example :
Yoan : What did you usually do on holidays ?
Lia : I would visit my grandparents In the village, but how not anymore.
 
Would + Mind + V-ing
Use would to express polite request.
Example :
Mrs. Lady : Would you mind posting the letter ?
Nita : No, Not at all.
 
Should + Verb base
Example :
Nisa : Ima , you should go to library now ?
Ima : Okay