Use past unreal conditionals to talk about how you would have acted differently if you had had more information. Basically, if I had known A, I would have done B. Imagine you brought chocolate for a co-worker. You didn't know it at the time, but your co-worker was diabetic. In this situation, you could say, "If I had known you were diabetic, I would not have brought chocolate."

Some Americans use the simple past in the if clause of a past unreal conditional. For example, there's an old song called, "If I knew you were coming, I'd have baked a cake." In formal speech or writing the correct form is, "If I had known you were coming, I would have baked a cake." There is often a difference between how grammar is taught and how ordinary people use it in conversation.

A conditional sentence can start with the if clause, or the result clause. In the classic American film It's a Wonderful Life, the main character George Bailey is thinking about killing himself. In a moment of sadness, George says that life would have been better if he had never been born. Listen to this dialog between George and his guardian angel, Clarence.

Clarence: So you still think killing yourself would make everyone feel happier?

George: Well I don't know. I guess you're right. I supposed it would've been better if I'd never been born at all.

Clarence: What did you say?

George: I said I wish I had never been born.

Notice how George puts the result clause first when he says, "I suppose it would have been better if I had never been born." George also shortens "would have" to "would've" and "I had" to "I'd." Native speakers often use contractions with the words "had" and "have." That means a past unreal conditional will often have two contractions in it — an extra challenge for English learners.

Sometimes speakers want to express how something that did not happen in the past has an effect in the present. For example, "If I had been born in China, I would speak Chinese." Or "If had quit university, I would not have this job." These are called mixed conditionals. In a mixed conditional, the if clause remains in the past perfect. But the result clause changes to the simple present to emphasize the effect in the present.

To emphasize a feeling of regret, add "only" to the if clause. Listen to this sad song by country singer Reba McEntire.

"If I had only known it was the last walk in the rain,
I'd keep you out for hours in the storm."

This song is an example of a mixed conditional. The if clause "If I had only known it was the last walk in the rain" is in the past perfect. But the result clause, "I'd keep you out for hours in the storm" is in the simple present. The singer is emphasizing her present feelings about something that did not happen in the past.

Past unreal conditionals are complex grammar structures. Make sure you have mastered the past perfect, the present perfect, and irregular verbs before studying advanced conditionals. For a simpler lesson on conditionals, see our previous episode of Everyday Grammar called "Introducing Conditionals."

When you are ready, a good way to practice past unreal conditionals is to ask your English-speaking friends if they have any regrets. You could ask "If you could change something about your past, what would you change?"