GRAMMAR RESOURCE · CHAPTER 22 · PART C

Conditional Sentences

Learn zero, first, second, third and mixed conditionals, including tense patterns and common exam traps.

Learning objectives

By the end of this lesson, you should be able to explain the rules, recognise the target forms in context, avoid common errors and apply the patterns to new sentences.

1. The basic conditional pattern

A conditional sentence links a condition (if-clause) with a result clause. The verb form depends on whether the meaning is general, possible, hypothetical or counterfactual.

If you heat ice, it melts.

2. Zero and first conditionals

Use the zero conditional for general truths and routines. Use the first conditional for realistic future possibilities; normally use a present form in the if-clause, not will.

Zero: If water reaches 100°C, it boils. First: If it rains, we will stay home.

3. Second conditional

Use if + past form with would/could/might + base verb for an unreal or unlikely present/future situation. Were is common in formal hypothetical clauses with all subjects.

If I were free, I would join you.

4. Third and mixed conditionals

The third conditional imagines a different past: if + past perfect, would have + past participle. Mixed conditionals connect a past condition to a present result or vice versa.

If she had left earlier, she would have caught the train.

5. Common mistakes

Avoid will in the ordinary if-clause of a first conditional. Do not confuse would have with the past perfect in the if-clause. Use unless only when the intended meaning is if not.

Correct: If he studies, he will pass. / If I had known, I would have called.

Guided practice

Try each item first. Then open the answer key and read the explanation for any answer you missed.

  1. Complete the zero conditional: If you mix blue and yellow, you ___.
  2. Complete: If it rains tomorrow, we ___ at home. (will stay / would stay)
  3. Choose: If I ___ you, I would apologise. (was / were)
  4. Complete: If she had studied, she ___ the exam. (would pass / would have passed)
  5. Correct: “If he will come, I will tell him.”
  6. Which conditional expresses a general truth?
  7. Complete: If I had taken the job, I ___ in London now.
  8. Complete: If you ___ harder, you would improve. (practise / practised)
  9. Rewrite using unless: “If you do not hurry, you will be late.”
  10. Complete: If they had left earlier, they ___ the train. (would catch / would have caught)
  11. Choose the correct form: If I ___ enough money, I would buy a laptop. (have / had)
  12. Does “If you heat ice, it melts” describe a fact or an unreal situation?
  13. Complete: If you had called me, I ___ you. (could help / could have helped)
  14. Correct: “Unless you don't study, you will fail.”
  15. Complete: If she were more careful, she ___ fewer mistakes.
Show answer key and explanations
  1. get green — Zero conditional describes a general result; present simple is used in both clauses.
  2. will stay — A realistic future possibility takes the first conditional.
  3. were — Were is the conventional form in hypothetical advice.
  4. would have passed — The third conditional imagines a different past result.
  5. If he comes, I will tell him. — The ordinary first-conditional if-clause uses a present form.
  6. Zero conditional — It describes facts, rules or regular results.
  7. would be — This mixed conditional links an unreal past condition with a present result.
  8. practised — Second conditional uses a past form in the if-clause for a hypothetical situation.
  9. Unless you hurry, you will be late. — Unless means if not.
  10. would have caught — Third conditional result: would have + past participle.
  11. had — The second conditional uses a past form for an unreal or unlikely situation.
  12. A general fact — Both clauses use present simple in the zero conditional.
  13. could have helped — Could have + past participle expresses a possible alternative past result.
  14. Unless you study, you will fail. (if the intended meaning is that studying prevents failure) — Unless already means if not, so an extra negative may reverse the intended meaning.
  15. would make — Second conditional result uses would + base verb.

Revision checklist

If an answer was wrong, identify the rule behind the mistake and try writing two original examples.

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Editorial note: Some grammar conventions vary by dialect or examination syllabus. Follow the terminology and conventions specified by your course or exam board where relevant.