How do you form the third conditional tense in English?

The third conditional requires us to construct a sentence in two parts.

We make the third conditional by using 'if,' the past perfect form of the verb in the first part of the sentence and then 'would have' and the past participle the second part of the sentence:

• if + past perfect, …would + have + past participle

It talks about the past. It's used to describe a situation that didn't happen, and to imagine the result of this situation.

• If he had studied, he would have passed the exam (but, really we know he didn't study and therefore he didn't pass)
• If I hadn't spent so much money in my 20's, I wouldn't have been poor in my 30's (but I did spend a lot, and so I did become poor).
• If we had taken the subway, we wouldn't have missed the plane (but we did not take the subway, and we did miss the plane)
• I wouldn't have been tired if I had gone to bed earlier (but I was tired because I did not go to bed earlier)
• I would have become a lawyer if I had followed my parents' wishes (but I did not become a lawyer and did not follow my parents' wishes)
• He would not have felt sick if he had not eaten the questionable street food (but he did eat the questionable street food and so he felt sick)

I hope that these examples help. If you have questions, comments, or would like to try your own examples, leave a comment on the blog post at https://gonaturalenglish.com/third-conditional