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 in the past would have been different if we knew that information.
This sentence pattern has exactly the same meaning as "If I had known that...". Only the word order is different. The two examples below are exactly the same.
- Had I known that Mark lived in Chicago, I would have called him when I was there.
- If I had known that Mark lived in Chicago, I would have called him when I was there.
It is more common to use "If I had known that...", but "Had I known that..." is used sometimes and it is definitely worth knowing. Had I known (that) + unknown fact + (then) different action
- Had I known that housing prices would drop, I wouldn't have bought a home last year.
- Had I known it would be so busy, I would have come earlier.
- Had I known that it was her birthday, I would have bought her a present.
- Had I known that it would be on sale this week, I would have waited to buy it.
- Had I known you were a vegetarian, I wouldn't have made chicken for dinner.
- Had I known that he wasn't coming, I wouldn't have made so much food.
- Had I known our class was canceled today, I would have stayed in bed.
We can also switch the order of the sentence. Different action + had I known (that) + unknown fact
- I would have invited you to the concert had I known you were a fan of the band.
- I could've helped him had I known that he needed help.
- We would never have bought this house had we known that we would have 5 children.
We can also use different subjects.
Bonus Tips and Points
- She would have joined that company had she known that it would be very successful.
- They wouldn't have gone to the beach had they known it was going to rain.
- Had she known her ex-boyfriend was at the party, she would never have shown up.
- Had he known that he would lose all his money, he would never have invested in that company.
- Had she known that he was the CEO, she wouldn't have argued with him.
1. We only use "were" with these sentences because these sentences are past unreal conditionals. Do not use the word "was" with unreal conditionals.
- Had I known he were coming, I would have made more food.
- Had I known it were raining, I wouldn't have gone.
- If she were here, we might have won the game.
2. We can also use the sentence pattern in this lesson when we are asking a question. We do this when we want to ask somebody if they would do something again if they had a chance to do it again.
- Had you known it would rain, would you have come?
- Had you known that your ex-girlfriend would be here, would you have come?
3. We typically use "would + verb", "was/were going to + verb", or "was/were + noun/adjective", or past tense verbs when talking about the information we did not know.
Real-World English Conversations
- Had I known it would rain, I wouldn't have come.
- Had I known it were going to be busy, I wouldn't have come.
- Had I known it were closed, I wouldn't have come to the store.
- Had I known she liked it, I would have got her one.
A) Had I known that I would get fired for saying that, I probably wouldn't have said it.
B) What do you mean "probably"?
A) I might have said it even if I knew that I would get fired because I was so mad at my boss at the time.
A) Why did you buy that at the mall? It is cheaper online.
B) Had I known that, I would've bought it online.
A) Everything is cheaper online. You should always check before you buy anything.
B) Well, had you come shopping with me like I asked you to, then you could have told me that. So, it is kind of your fault.
A) Are you serious?
B) I am just joking, but I really do wish you would have come with me.
A) Had I known that the beach by the hotel would be so busy, I would have booked a different hotel.
B) I agree. I am surprised that none of the reviews online said anything about that. 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 them at home and in real life, and make sure to come back to review the material so you do not forget.