Zero Conditional
An A2 guide to the zero conditional — using "if" or "when" with the present simple to talk about facts, scientific truths, and habits that are always true.
What Is the Zero Conditional?
The zero conditional is a sentence with two parts joined by if or when. We use it to talk about things that are always true: facts, scientific truths, and habits.
If you heat water to 100°C, it boils.
When the sun goes down, it gets dark.
If I drink coffee at night, I can't sleep.
Both halves of the sentence use the present simple.
| Part 1 | Part 2 |
|---|---|
If/when + present simple | present simple |
If you heat ice, | it melts. |
When I am tired, | I go to bed early. |
Form
If / When + subject + present simple, subject + present simpleYou can also flip the order — there is no comma in the middle when the result comes first.
Ice melts if you heat it.
It gets dark when the sun goes down.
When the if/when clause comes first, use a comma. When it comes second, no comma.
| Order | Example |
|---|---|
If first | If you press this button, the light comes on. |
If second | The light comes on if you press this button. |
When to Use the Zero Conditional
1. Scientific facts and general truths
If you mix red and blue, you get purple.
Water freezes when the temperature drops below 0°C.
Plants die if they don't get water.
2. Habits and routines
If I have time, I read before bed.
When I go to the gym, I always run for 20 minutes.
I drink tea if I feel tired.
3. Instructions and rules
If the alarm rings, leave the building.
When the door is locked, use this key.
”If” vs. “When”
In the zero conditional, if and when often mean almost the same thing. Both work for things that are always true.
If you press the button, the door opens. ✓
When you press the button, the door opens. ✓
But there is a small difference:
| Word | Feels like | Example |
|---|---|---|
if | ”every time this might happen” | If it rains, I take an umbrella. |
when | ”every time this does happen” | When it rains, I take an umbrella. |
For A2 level, use whichever sounds natural. Both are correct.
Common Mistakes
| Mistake | Better | Why |
|---|---|---|
If you will heat water, it boils. | If you heat water, it boils. | Don’t use will in the if part of a zero conditional. |
If I am tired, I will go to bed early. (every day) | If I am tired, I go to bed early. | For habits/general truths, use present simple in both parts. |
If you mix red and blue you get purple. | If you mix red and blue, you get purple. | Add a comma when the if clause comes first. |
If water boils when you heat it to 100°C. | Water boils when you heat it to 100°C. | Use only one of if or when, not both. |
If the light is green, you crossing the street. | If the light is green, you cross the street. | Use the present simple, not -ing. |
Practice: Exercises
If you heat water to 100°C, it ___.
Summary
The zero conditional describes things that are always true: facts, science, habits, and rules.
The form is: If/when + present simple, present simple.
Use a comma when the if/when clause comes first; no comma when it comes second.
If you mix yellow and blue, you get green.
You get green if you mix yellow and blue.
Both if and when are usually fine. Don’t use will in the if part of a zero conditional.