Before doing the conditional/hypothetical sentences, you need to review past modal verbs and the past perfect tense.
Past Modals for Single Actions in the Past: The Simple Past Tense
The past tense of must, have to, and has to is HAD TO.
Had to Obligation or necessity in the past Past of must,
(hadda) have to, and has to
He had to take his daughter to the hospital
last night because she had a high fever.
He had to change the flat tire on his car last night.
We had to pay our income taxes last year before April 15th.
I had to drive my wife downtown because she is afraid to drive in
the city by herself.
________ _______________________________ ____________
Must have + past participle Past conclusion or supposition only;
(musta) Never a past obligation: For past
obligations, use had to.
Sara is a teacher; therefore, she must have graduated from a four-year college.
There was some candy on the table and the children were in the room. Now the candy is gone. The children must have eaten the candy. (conclusion)
She broke her leg playing basketball. It must have hurt a lot. (conclusion)
When I came home last night, the house was very clean. My wife must have done a lot of housework during the day. (conclusion)
While I was driving home, I got a flat tire, so I had to use my spare tire. (obligation)
The boy cut his head badly, so he had to go to the hospital. (obligation)
The toilet broke last night, so I had to fix it right away. (obligation)
Might have + past participle Past situation -- maybe it happened,
May have + past participle maybe it didn't. We don't know for sure,
Could have + past participle but we do know that it was possible.
(mighta, maya, coulda)
The student didn't come to class yesterday. She might have gone to the doctor's. She might have had an accident. She may have gone shopping. She could have stayed in bed. I don't know what happened for sure, but all of the above are possible.
My friend bought a lottery ticket. He could have had the winning ticket, but I am not sure. It might have snowed in the mountains last night. Then again, it might not have snowed.
Could have + past participle Past ability or capability to do something,
(coulda) but you chose not to do it. You had the
opportunity to do something, but you
decided not to do it.
A past possibility that you had an opportunity to do, but you chose not to do.
I lived in Asia for over 5 and a half years, but I never went to Korea. I could have gone there many times, but never did.
I could have stayed in Europe in 1973, but I decided to return to the United States instead.
I could have become a history teacher if I had wanted to, but I decided to become an English teacher instead.
You could have skipped school today if you had wanted to, but you decided to come.
My wife and I could have gone to a movie last night, but we were too tired and decided to bag it and not go.
Should have + past participle Past obligation which you didn't
(shoulda) do. Something was the correct or right action to
do, but you didn't do it. Something was a good
idea or thing to do in the past, but you didn't do
it. In other words, you made a mistake.
You were speeding in a car and a policeman saw you and gave you a speeding ticket. You should have slowed down, but you didn't.
You had a test last week, but you didn't study for it and you failed it. You should have studied for it, but you didn't.
My son went outside without his coat in the rain last week and he caught a bad cold. He should have worn a coat, but he didn't.
The students shouldn't have cheated on the exam, but they did.
I should have learned how to type when I was in high school, but I didn’t. As a result, I am a slow typist.
America shouldn’t have gotten into a war with Iraq, but it did.
Those boys shouldn’t have teased the new student in the class. He started to cry and then everyone felt bad for him.
Past Perfect Tense: Used to describe two related actions or activities that happened at different times in the past. Its emphasis is on showing the relationship of the actions relative to which one happened first and which one happened second. The past perfect is used with the action that happened first; the simple past is used with the action that happened second. It simply says, "First this thing had begun and ended, and then this other thing began and ended." Note: Most native speakers tend not to use the past perfect. It can be avoided by using words such as before, after, first, then, next, afterwards, etc. and using the simple past tense to express both actions. Also, if something logically comes before something else, then native speakers avoid using the past perfect. It is not necessary.
We had finished dinner when our friends stopped by for a visit.
My wife had graduated from the university when we met in 1979.
The students had taken the entrance examination when they received permission to register for class.
I had taken out the trash by the time my wife returned home from shopping.
I had finished university when I went into the army.
The students had finished the examination when John arrived in the room.
More on the Past Perfect Tense
The past perfect tense is used when two or more actions happened in the past at different times. One action began and ended in the past before another action began and ended in the past at a different time. The action further in the past (the action that happened first) uses the past perfect tense. The action that happened second uses the simple past tense. Also, th4e past perfect is ued in conditionl/hypothetical sentences when the condition in the past didn’t happen and as a result it didn’t actually happen.
Also, do not use the past perfect tense when talking about only one action.
Moreover, don’t use the past perfect if one action of naturally occurs before another action.
Examples of two actios in the past at different times:
I had graduated from university when I was drafted into the US Army.
After I graduated from university, I was drafted into the US Army.
I had taught for four hours by the time I went home.
After I taught for four hours, I went home.
Unreal Past Conditional/Hypothetical Examples:
If I had been born in Vietnam I would have spoken Vietnamese perfectly all my life.
I wasn’t born in Vietnam, I have never spoken Vietnamese.
If my friend hadn’t drunk so much whiskey last night, he wouldn’t have felt sick this morning.
He drank too much whiskey last night and he did feel sick this morning.
Past Perfect Tense Form
First Action Second Action
We eaten simple past tense
They had started
First one action began and finished.
I got up.
Next, another action began and finished.
I drank two cups of coffee.
After I got up, I drank two cups of coffee.
An Unreal Condition An unreal result
I went into the army in 1967. I went to Vietnam in 1968. Both of these sentences are true.
If I hadn’t gone into the army in 1967, I wouldn’t have gone to Vietnam.
Class One and Two were taught in Book Four on 4.7.