What is the Third Conditional in English?

The Third Conditional is a grammar structure we use to talk about imaginary situations in the past. These situations did not happen, and therefore their results also did not happen.

We use it to express regret, criticism, or to simply imagine a different past. It’s like looking back and saying, ‘What if…?’

How Do You Form the Third Conditional?

The Third Conditional has two parts: the 'if' clause and the main clause. Each clause uses a specific verb tense.

• The 'if' clause uses the past perfect tense. This describes the imaginary past condition.
• The main clause uses would have + past participle. This describes the imaginary past result.

The general structure is: If + Subject + had + past participle, Subject + would have + past participle.

You can also put the main clause first, but remember not to use a comma if the 'if' clause comes second.

• If I had known, I would have helped.
• I would have helped if I had known.

When Do We Use 'Should Have + Past Participle'?

We use should have + past participle to talk about something that was a good idea in the past but didn't happen, or something that happened but was a bad idea.

• Regret: Expressing sadness or disappointment about a past action or inaction. I should have studied more for the exam. (I didn't study enough, and I regret it.)
• Criticism: Saying that someone (including yourself) made a mistake in the past. You shouldn't have told her my secret. (It was wrong of you to tell her.)
• Missed Opportunity: Talking about something that was possible but didn't happen. We should have left earlier. (We had the chance, but we didn't, and now we're late.)

The structure is always should + have + past participle. For the negative, it's shouldn't + have + past participle.

Can We Use Other Modals in Conditionals?

Yes, in the main clause of the Third Conditional, you can use could have + past participle or might have + past participle instead of would have + past participle.

• Could have suggests a past possibility or ability. If I had saved money, I could have bought a new car.
• Might have suggests a past possibility, but with less certainty than would have. If it hadn't rained, we might have gone to the beach.

Also, in the 'if' clause, you can sometimes use the past perfect continuous for ongoing actions. If I hadn't been working all day, I would have joined you.

What Are Mixed Conditionals?

Mixed conditionals combine parts of different conditional types to talk about complex past and present relationships.

• Past condition, present result: If + past perfect (Third Conditional 'if' clause) + would + base verb (Second Conditional main clause). This means a past action (that didn't happen) has a result now. If I had taken that job, I would be rich now. (But I didn't take the job, so I'm not rich now.)
• Present condition, past result: If + simple past (Second Conditional 'if' clause) + would have + past participle (Third Conditional main clause). This means a present situation (that is not true) affected something in the past. If I spoke French, I would have understood them yesterday. (But I don't speak French, so I didn't understand them yesterday.)

Examples

• If she had known about the traffic, she would have left earlier.
• They wouldn't have missed the flight if they had woken up on time.
• I should have called my mother yesterday.
• You shouldn't have eaten all the cake!
• If he hadn't been wearing a helmet, he might have been seriously injured.
• We could have gone to the concert if we had bought tickets in advance.

Practice

Common mistakes for Spanish speakers

Spanish speakers often make specific mistakes with these structures due to direct translation:

• Third Conditional: A common error is using would have in the 'if' clause. For example, If I would have known... is incorrect. The correct form is If I had known... (using the past perfect). Remember, would is for the main clause.
• 'Should have': Sometimes learners confuse should have with must have. Should have expresses regret or criticism about a past action. Must have expresses a strong deduction or certainty about something that happened in the past. For example, He must have left means 'I'm sure he left,' not 'He made a mistake by leaving.'
• Incorrect Verb Form: Ensure you always use the past participle after have (e.g., should have gone, not should have go or should have went).

Frequently asked questions

What is the main difference between the Second and Third Conditional?

The Second Conditional talks about imaginary situations in the present or future (If I had money, I would buy a car.). The Third Conditional talks about imaginary situations in the past (If I had had money, I would have bought a car.).

Can I use 'd instead of 'had' or 'would'?

Yes, 'd is a common contraction for both had and would. In the 'if' clause, If I'd known... means If I had known.... In the main clause, I'd have gone... means I would have gone.... Context usually makes it clear.

Does 'shouldn't have + past participle' mean the same as 'didn't have to'?

No, they are different. Shouldn't have + past participle means something happened that was a mistake or bad idea (You shouldn't have lied.). Didn't have to + base verb means something was not necessary, but it might have happened anyway (I didn't have to work yesterday.).

Are these structures formal or informal?

Both the Third Conditional and should have + past participle are standard English structures. They are used in both formal and informal contexts, depending on the situation. They are essential for fluent B2 communication.

Related lessons

• Conditionals
• Conditionals
• Conditionals
• Conditionals