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Zero and First Conditional

Level: A2 · Free grammar guide

H1: Zero and First Conditional

Direct answer

Use the Zero Conditional for things that are always true — general facts, scientific truths, habits. Use the First Conditional for real future possibilities — things that might happen. Both use the Present Simple in the if clause; the difference is the result clause.

The rule / form box

Zero Conditional — general truths

First Conditional — real future possibility

Both orders work:

Future time clauses: After when, as soon as, until, before, after, use Present Simple for future meaning, not will: When I arrive, I will call you. (Not: When I will arrive...)

Comparison table

Zero ConditionalFirst Conditional
MeaningAlways true, general factReal future possibility
FormIf + Present Simple, Present SimpleIf + Present Simple, will + base verb
ExampleIf you mix red and blue, you get purple.If you mix these colours, you will get purple.
TimeAny time / alwaysFuture
How likely?100% — a factPossible — it might happen

Zero vs First for general truths: Both can describe general truths. If you heat water, it boils (zero — a scientific fact). If you heat the water, it will boil (first — the same fact, framed as a prediction about what will happen). The difference is emphasis, not correctness. When the situation is clearly in the future, First Conditional is more natural: If you heat the water now, it will boil in two minutes.

Examples (10)

  1. If you press this button, the machine starts. (Zero — always true.)
  2. If you press that button, you will start the machine. (First — a prediction about this moment.)
  3. If it rains, the grass gets wet. (Zero — general fact.)
  4. If it rains tonight, we will cancel the barbecue. (First — a future plan.)
  5. If I drink coffee late, I can't sleep. (Zero — a personal habit.)
  6. If I drink coffee now, I won't sleep tonight. (First — tonight's result.)
  7. If you don't water plants, they die. (Zero — always true.)
  8. If you don't water the plants this week, they will die. (First — this week's future.)
  9. When the bell rings, the lesson ends. (Zero — routine.)
  10. When I finish this book, I will start a new one. (First — future plan, when + Present Simple.)

    11. Common mistakes

    ❌ If it will rain, we will stay home.

    ✅ If it rains, we will stay home. (In the if clause, use Present Simple, not will — even for future meaning.)

    ❌ If you heat water, it will boils.

    ✅ If you heat water, it boils. / it will boil. (After will, use the base verb (boil, not boils). Zero and first conditional are both fine here.)

    ❌ If I will see him, I tell him.

    ✅ If I see him, I will tell him. (If clause: Present Simple. Result: will + base verb.)

    ❌ When I will arrive, I will call you.

    ✅ When I arrive, I will call you. (After when for future meaning, use Present Simple.)

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    Exercises (16)

    Instructions: Choose the correct answer. Each answer shows an explanation.

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    Exercises

    Choose the correct answer. You will see the explanation after checking.

    1. If you ___ water to 100°C, it ___.
    2. If it ___ tomorrow, we ___ at home.
    3. If I ___ late, my teacher ___ angry.
    4. If you ___ hard, you ___ the exam.
    5. If she ___ the bus, she ___ late for work.
    6. If you ___ ice in the sun, it ___.
    7. When I ___ home, I ___ you.
    8. If the weather ___ nice, we ___ a picnic.
    9. If you ___ too much sugar, you ___ weight.
    10. If I ___ time, I ___ you with your homework.
    11. Choose the correct sentence:
    12. If you ___ this button, the light ___ on.
    13. She ___ you when she ___.
    14. If we ___ now, we ___ on time.
    15. If you ___ the oven now, the cake ___.
    16. If I ___ the answer, I ___ you tomorrow.

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