Some things are just always true: at sea level, water boils at 100°C, plants die without sunlight, and ice melts when you heat it. English has a neat structure for this kind of automatic cause-and-effect: the zero conditional.
Quick form: If / When + present simple, present simple → If you heat ice, it melts. When it rains, the ground gets wet.
What the zero conditional expresses
The zero conditional describes things the speaker presents as a rule, fact, routine, or normal consequence — not a specific future event:
- Scientific facts: If water reaches 100°C at sea level, it boils.
- Natural laws: Plants die if they don't get enough light.
- General habits or routines: When I'm tired, I make mistakes.
- Instructions with built-in consequences: If you press this button, the door opens.
The key idea is that the speaker is stating how things generally work, not predicting a particular future outcome.
Forming the zero conditional
The basic zero conditional uses present simple in both clauses:
| Clause | Tense | Example |
|---|---|---|
| If / When clause | present simple | If you heat ice… |
| Result clause | present simple | …it melts. |
The structure works in either order:
If/when + present simple, present simple (comma after the if/when clause) If you mix red and blue paint, you get purple.
Present simple + if/when + present simple (no comma when the if/when clause comes second) You get purple if you mix red and blue paint.
Both sentences mean the same thing. When writing, a comma after an initial if/when clause is the standard convention; when the if/when clause comes second, a comma is usually omitted.
There is a closely related instruction pattern: if + present simple, imperative (If the alarm rings, leave the building.). The imperative result clause is natural for advice and instructions. See the Instructions with if section below.
If vs. when
Both if and when work in the zero conditional, and in many cases either is fine. The difference is in emphasis:
- When presents the condition as expected or known to happen: When I drink coffee late, I can't sleep. (this regularly happens)
- If presents it simply as a condition: If you eat too much sugar, you feel sick. (a general truth)
For scientific facts and general rules, you will often see both. For personal habits and routines, when tends to sound more natural.
Instructions: if + present simple, imperative
The result clause can be an imperative (a command or instruction) instead of the present simple:
- If you feel sick, rest at home.
- If the light turns red, stop.
- Call me if you need help.
This pattern is very common for instructions and advice: the if-clause states the condition; the imperative tells what to do.
Zero conditional vs. first conditional
Both use if, but with a different meaning:
| Zero conditional | First conditional |
|---|---|
| If you heat water to 100°C, it boils. | If you heat the soup, it will taste better. |
| A general rule or fact | A future consequence, prediction, or warning |
| Present simple + present simple | Present simple + will + base verb |
The zero conditional presents the result as a general rule. The first conditional presents the result as a future consequence or possibility in a specific situation.
No will in the if-clause for time and condition clauses. A very common mistake is using will in the if/when clause. For both zero and first conditionals, the condition clause uses the present simple:
❌ If it will rain, the ground gets wet. → ✅ If it rains, the ground gets wet.
Will belongs in the result clause of the first conditional (If it rains, I will stay home.). There is a rare advanced case where will after if expresses willingness (If you will wait a moment…), but that is not the zero or first conditional — learners can explore it later.
Common mistakes
- ❌ If you will mix red and blue paint, you get purple. → ✅ If you mix red and blue paint, you get purple. (no will in the if-clause)
- ❌ If water reaches 100°C, it is boiling. → ✅ If water reaches 100°C, it boils. (present simple, not continuous, for a general rule)
- ❌ If I'm tired, I always am making mistakes. → ✅ If I'm tired, I always make mistakes. (present simple for a general pattern; frequency adverbs like always go before the main verb)
- Note: If you mix yellow and blue paint, you will get green is grammatically correct as a first conditional (making a prediction), but you get green is more natural when stating it as a general rule.
Quick check
Which form fits?
- If you freeze water, it ____ (turns / will turn) to ice.
- ____ (If / When) I'm stressed, I go for a walk. (which fits better here?)
- If the alarm rings, ____ (leave / you will leave) the building immediately.
- Ice melts if you ____ (heat / will heat) it.
- If you mix yellow and blue paint, what colour ____ (do you get / will you get)?
Show answers
- turns — zero conditional for a scientific rule; will turn is also possible if you think of it as a first conditional prediction, but turns is more natural for a fact
- When — fits better for a personal routine that actually happens; if is also possible but sounds slightly more hypothetical
- leave — imperative: natural for instructions (if + present simple, imperative)
- heat — no will in the if-clause; present simple throughout
- do you get — asks about a general rule (zero conditional); will you get works as a first-conditional question, but do you get is more natural when asking about a fact
Key takeaways
- The basic zero conditional uses present simple in both clauses: If / When + present simple, present simple.
- Use it when presenting something as a general rule, fact, habit, or automatic consequence — not as a specific future event.
- When presents the condition as expected or regular; if presents it simply as a condition — both often work.
- A related instruction pattern uses an imperative in the result clause: If you're late, call me.
- No will in the if/when-clause for time and condition clauses. Put will in the result clause if you're using the first conditional for a future consequence.