This expression is used when we are talking about something we did not know in the past, but we wish had known it at the time. Our action would have been different if we knew that information. Real situation:
I went hiking. It started to rain a lot while I was hiking. But, before I went hiking, I didn't know that it was going to rain. My thoughts now:
If I had known that it would rain, then I would not have gone hiking. If I had known (that) + unknown fact + (then) different action
Use "would/could/might have + past participle" for the "different action".
- If I had known that this sweater would be on sale this week, then I wouldn't have bought it last week.
- If I had known he would be at the party, then I wouldn't have come.
- If I had known the test was going to be so hard, then I would have studied harder.
- If I had known that you were moving to a new house, I could have helped you move.
- If I had known that I could buy it online, then I wouldn't have bought it at the mall.
- If I had known it would rain, I never would have gone to the parade.
We can also switch the order of the sentence. Different action + if I had known (that) + unknown fact
- I could have slept longer if I had known that you were going to be an hour late.
- I might have gone to the party if I had known that you were going to be there.
- I would have helped you if I had known that you were in trouble.
- I wouldn't have eaten it if I had known it was yours.
- I couldn't have finished this if you had not helped me.
- I might have died if they hadn't saved me.
We can also use different subjects.
Bonus Tips and Points
- If she had known that, I am sure that she would have behaved differently.
- If he had arrived on time, then he wouldn't have been scolded by his teacher.
- She wouldn't have become a doctor if she had known that she was afraid of blood.
- They said they could have met us if they had known that we were in town.
- We wouldn't have moved here if we had known that the neighbors would be so noisy.
1. Typically, we use "would + verb", "was/were going to + verb", or "was/were + noun/adjective" when talking about the information we did not know.
- If I had known that it would rain, I wouldn't have gone.
- If I had known that the show was going to be canceled, I wouldn't have come.
- If I had known it were rainy, I would've brought an umbrella.
Some people use "were" with every subject when using unreal conditionals like this.
- If I had known he were coming, I wouldn't have come.
We normally use "he was", but with unreal conditionals, we usually use "were" with every subject. To be honest, you can use both "was" or "were". English speakers do not pay much attention to this and can understand both.
2. We typically use "would/could/might + have + past participle" to talk about the alternative action in the past.
Real-World English Conversations
- If I had known you were going, I would have gone too.
- If I had known that he talked behind my back, I wouldn't have helped him.
- If I had known that the class were canceled, I could have slept in.
- If I had known that it was going to rain, I might have stayed home.
A) Why are you late?
B) Traffic was awful.
A) Traffic is always awful at this time.
B) I usually don't drive at this time. If I had known that, then I would've left earlier.
A) I'm so hungry. Do you want to get something to eat?
B) Actually, I just ate. I'm sorry. If I had known that you were hungry, I would have brought you something.
A) Your dog is so cute.
B) Thanks, but to be honest, if I had known how hard it was to take care of a dog, I probably wouldn't have gotten one.
A) If I had known that you were going to be in such a bad mood, I never would have come to meet you today.
B) I'm sorry. I had a terrible day. I'll try to be better. Study these free English lessons to improve your English speaking. If you learn these common sentence patterns well, then your English speaking will improve greatly and you will be able to have fluent conversations in English in the near future! Study the lessons well, practice using the sentences and questions at home and in real life, and make sure to come back to review the material so you do not forget. If you do these three things, then you will be speaking English like a native English speaker in no time!