Past Conditionals

Past Real Conditional

FORM

[If / When ... Simple Past ..., ... Simple Past ...]
[... Simple Past... if / when ... Simple Past ...]

USE

The Past Real Conditional describes what you used to do in particular real-life situations. It suggests that your habits have changed and you do not usually do these things today.

Examples:

• If I went to a friend's house for dinner, I usually took a bottle of wine or some flowers. I don't do that anymore.
• When I had a day off from work, I often went to the beach. Now, I never get time off.
• If the weather was nice, she often walked to work. Now, she usually drives.
• Jerry always helped me with my homework when he had time. But he doesn't do that anymore.
• A: What did you usually do when it rained?
  B: I usually stayed at home.
  

IMPORTANT Used to

The form "used to" expresses the idea that something was an old habit that stopped in the past. This form is commonly used in Past Real Conditional sentences to emphasize that something was a habit. The examples below have the same meaning as the examples above.

Examples:

• If I went to a friend's house for dinner, I used to take a bottle of wine or some flowers. I don't do that anymore.
• When I had a day off from work, I used to go to the beach. Now, I never get time off.
• If the weather was nice, she used to walk to work. Now, she usually drives.
• Jerry used to help me with my homework when he had time. But he doesn't do that anymore.
• A: What did you usually do when it rained?
  B: I used to stay at home.
  

IMPORTANT If / When

Both "if" and "when" are used in the Past Real Conditional. Using "if" suggests that something happened less frequently. Using "when" suggests that something happened regularly.

Examples:

• When I had a day off from work, I usually went to the beach.
  I regularly had days off from work.
• If I had a day off from work, I usually went to the beach.
  I rarely had days off from work.

Past Unreal Conditional

FORM

[If ... Past Perfect ..., ... would have + past participle ... ]
[... would have + past participle ... if ... Past Perfect ...]

USE

The Past Unreal Conditional is used to talk about imaginary situations in the past. You can describe what you would have done differently or how something could have happened differently if circumstances had been different.

Examples:

• If I had owned a car, I would have driven to work. But I didn't own one, so I took the bus.
• She would have traveled around the world if she had had more money. But she didn't have much money, so she never traveled.
• I would have read more as a child if I hadn't watched so much TV. Unfortunately, I did watch a lot of TV, so I never read for entertainment.
• Mary would have gotten the job and moved to Japan if she had studied Japanese in school instead of French.
• If Jack had worked harder, he would have earned more money. Unfortunately, he was lazy and he didn't earn much.
• A: What would you have done if you had won the lottery last week?
  B: I would have bought a house.
• A: What city would you have chosen if you had decided to move to the United States?
  B: I would have chosen Seattle.
  

IMPORTANT Only use "If"

Only the word "if" is used with the Past Unreal Conditional because you are discussing imaginary situations. "When" cannot be used.

Examples:

• I would have bought that computer when it had been cheaper. Not Correct
• I would have bought that computer if it had been cheaper. Correct

EXCEPTION Conditional with Modal Verbs

There are some special conditional forms for modal verbs in English:
would have + can = could have
would have + shall = should have
would have + may = might have
The words "can," "shall" and "may" cannot be used with "would have." Instead, they must be used in these special forms.

Examples:

• If I had gone to Egypt, I could have learned Arabic.
• If she had had time, she might have gone to the party.

The words "could," should," "might" and "ought to" include Conditional, so you cannot combine them with "would have."

Examples:

• If I had had more time, I could have exercised after work.
• If he had invited you, you might have gone.

EXERCISES AND RELATED TOPICS

• Conditional Exercise 4 Past Unreal Conditional
• Conditional Exercise 5 Past Real Conditional vs. Past Unreal Conditional
• Conditional Exercise 6 Present Unreal Conditional vs. Past Unreal Conditional 

SOURCE: http://www.englishpage.com/conditional/pastconditional.html