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 she had studied, she would have passed.
• I would have called you if I had known.

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. Recognising 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 1 (I/A)
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)

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