THIRD CONDITIONAL EXERCISE 1 (ESL)

level: Intermediate (B1/B2)

✓ Useful for Cambridge B2/C1

The third conditional is used to talk about unreal situations in the past — things that did not happen, and what the result would have been if they had. It follows a fixed structure: if + past perfect in the condition clause, and would have + past participle in the result clause. This is exercise 1 of 2 in this series.

Grammar review The third conditional describes an unreal past situation and its imaginary result. The past cannot be changed, this structure lets us speculate about how things could have been different.

Structure:
If + past perfect → would have + past participle

Examples:
• If he had left earlier, he would have caught the train.
• She would have visited us if she had had more time.

Both clause orders are correct. A comma follows the if clause when it comes first.

Variations:
• could have or might have can replace would have to express possibility rather than certainty.
• In formal writing, if can be dropped using inversion: Had she known, she would have acted.

Most common error:
Never use would have in the if clause.
✗ If I would have known…
✓ If I had known…

READY TO PRACTICE? LET’S GO!

Complete each sentence with the correct third conditional form of the verb in brackets.

🎓 The third conditional in Cambridge English exams The third conditional appears regularly in Cambridge exams at B2, C1, and C2 level. Here is where it matters most:

B2 First & C1 Advanced — Use of English, Part 4 (Key Word Transformations)
You must rewrite a sentence using a given key word while keeping the same meaning. Third conditional transformations are classic items — for example, converting a simple past sentence into an if…would have structure, or the reverse.

B2 First & C1 Advanced — Writing Tasks
Essays, reports, and proposals frequently call for hypothetical past reasoning: If the policy had been introduced earlier, the results would have been very different. Accurate use of the third conditional signals the grammatical range that earns top marks.

C2 Proficiency — Inverted form
At C2 level, the third conditional may appear without if, using inversion instead: Had she known, she would have acted sooner. Recognizing and producing this formal variant is expected at C2.

Key exam tip: Never use would have in the if clause — this is the most penalised error in Cambridge third conditional items.

More conditional exercises The first conditional 1 (B)
The first conditional 2 (B)
The first conditional 3 (B)
The second conditional 1 (I)
The second conditional 2 (I)
First or second conditional? 1 (I)
First or second conditional? 2 (I)
The third conditional 2 (I/A)
Conditional tenses (mixed) 1 (I)
Conditional tenses (mixed) 2 (I)
Conditional or future? 1 (I)
Conditional, future, or present? 1 (I)