Modals In The Past Form

Modals and Modality
Modal verbs are common auxiliary verbs in Germanic languages including English that indicate modality. Modality is the grammaticalized expression of the subjective attitudes and opinions of the speaker including possibility, probability, necessity, obligation, permissibility, ability, desire, and contingency.

The Modal Verbs in English

The nine modals verbs in English are:

•  can
• could
• may
• might
• must
• shall
• should
• will
• would

Position of Modal Verbs
Modal verbs always appear in the first position at the beginning of the verb phrase in English. Unlike other verbs, modal verbs do not show tense or number. The eight possible verb phrase combinations that contain modal verbs in English are:

• modal verb + base form = will eat
• modal verb + be + present participle = will be eating
• modal verb + have + past participle = will have eate 
• modal verb + be + past participle = will be eaten 
• modal verb + have + been + present participle = will have been eating
• modal verb + have + been + past participle = will have been eaten
• modal + be + being + past participle = will be being eaten
• modal verb + have + been + being + past participle = will have been being eaten

Double Modals
Although most varieties of English only allow for the use of one modal verb per verb phrase, some English dialects such as Southern American English allow for multiple modals. For example, the double modal might could as in He might could build a new machine shed expresses both possibility and ability. However, prescriptive grammars proscribe against the use of double modals.

Some Definitions of English Modal Verbs
Modal verbs are difficult to define in any language because of the wide range of pragmatic uses of modal verbs by native speakers. Some of the more common definitions (in no particular order) of the modal verbs in English are: 

• can – ability, permission, possibility, request
• could – ability, permission, possibility, request, suggestion
• may – permission, probability, request
• might – possibility, probability, suggestion
• must – deduction, necessity, obligation, prohibition
• shall – decision, future, offer, question, suggestion
• should – advice, necessity, prediction, recommendation
• will – decision, future, intention, offer, prediction, promise, suggestion
•  would – conditional, habit, invitation, permission, preference, request, question, suggestion

Examples of Modal Verb Usage
The following sentences are examples of usage of modal verbs in English. For example, the following four sentences all ask for permission but with different degrees and types of modality:

• Can I go to the bathroom? (asking for permission)
• May I go to the bathroom? (more politely asking for permission)
• Could I go to the bathroom? (asking for permission with less certainty)
• Might I go to the bathroom? (asking for permission with uncertainty)

The following sentences also demonstrate the subtle meanings in regards to modal verbs of suggestion: 

• You could listen to me. (suggestion)
• You might listen to me. (uncertain suggestion)
• You should listen to me. (strong suggestion)
• You must listen to me. (stronger suggestion)
• You will listen to me. (strongest suggestion)

The meanings of modal verbs are very pragmatic and must be learned through use.
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) 

Remember: "Could not" vs. "Might not"
"Could not" suggests that it is impossible for something to happen. "Might not" suggests you do not know if something happens. 
Examples:

• Jack might not have the key. Maybe he does not have the key.
• Jack could not have the key. It is impossible that he has the key.

2. 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 )

3. 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)

4. Shall
"Shall" is used to indicate future action. It is most commonly used in sentences with "I" or "we," and is often found in suggestions, such as "Shall we go?" "Shall" is also frequently used in promises or voluntary actions. In formal English, the use of "shall" to describe future events often expresses inevitability or predestination. "Shall" is much more commonly heard in British English than in American English; Americans prefer to use other forms, although they do sometimes use "shall" in suggestions or formalized language. 
Examples:

• Shall I help you? (suggestion)
• I shall never forget where I came from. (promise)
• He shall become our next king. (predestination)
• I'm afraid Mr. Smith shall become our new director. (inevitability)

5. 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)

6. Ought to
"Ought to" is used to advise or make recommendations. "Ought to" also expresses assumption or expectation as well as strong probability, often with the idea that something is deserved. "Ought not" (without "to") is used to advise against doing something, although Americans prefer the less formal forms "should not" or "had better not."
Examples:

• You ought to stop smoking. (recommendation)
• Jim ought to get the promotion. (It is expected because he deserves it)
• This stock ought to increase in value. (Probability)
• Mark ought not to drink so much. (advice against something (notice there is no "to")