What is the Zero Conditional?
The Zero Conditional is a conditional structure we use to talk about things that are always true — not just likely or possible, but guaranteed. If condition X is met, result Y happens every single time without exception. This makes it the perfect tool for stating facts, natural laws, habits, and general rules.
It is called "zero" because the possibility of the result happening is not zero — quite the opposite. The word "zero" refers to the fact that there is zero uncertainty: if the condition is true, the result is always true. Compare: "If you heat water to 100°C, it boils" (Zero Conditional — a law of physics, always true) vs "If you heat the soup, I will eat it" (First Conditional — a specific future promise).
The Zero Conditional describes a fixed relationship between cause and effect. The First Conditional describes a specific future possibility. Whenever you are stating something universally true, reach for the Zero Conditional.
How to Form the Zero Conditional
The Zero Conditional uses the Present Simple in both clauses — the if-clause (the condition) and the main clause (the result). Both clauses can come first; when the if-clause comes second, no comma is used.
IF + Subject + Present Simple, Subject + Present SimpleStructure
| Structure | Clause type | Example |
|---|---|---|
| If + Present Simple | Condition (if-clause) | If you heat ice, |
| Subject + Present Simple | Result (main clause) | it melts. |
Positive, Negative, and Question Forms
The clauses can appear in either order. When the result clause comes first, no comma is needed: "The machine stops if you press this button."
| Form | If-clause | Result clause |
|---|---|---|
| Positive | If you mix red and blue, | you get purple. |
| Negative | If you don't water plants, | they die. |
| Question | What happens | if you add salt to water? |
| Imperative result | If the alarm rings, | leave the building immediately. |
When to Use the Zero Conditional
Scientific facts and laws of nature
Use the Zero Conditional to express facts that are always true in nature, science, or physics. These are not predictions — they are certainties. The result happens every single time the condition is met, with no exceptions.
- If you heat water to 100°C, it boils.
- If plants don't get sunlight, they die.
- If you drop a heavy object, it falls to the ground.
General truths and universal rules
We use the Zero Conditional for things that are universally accepted as true — social rules, biological facts, or mathematical relationships. Not just natural laws, but any statement that is consistently and reliably true.
- If you add two and two, you get four.
- If people don't sleep enough, they feel tired.
- If you eat too much sugar, your teeth decay.
Habitual and routine cause-and-effect
When a particular condition reliably produces the same result in someone's personal experience or routine, the Zero Conditional works well. The focus is on the predictable pattern, not a specific future occasion.
- If I drink coffee after 8 p.m., I can't sleep.
- If she misses breakfast, she gets a headache.
- If the traffic is heavy, he takes the train instead.
Instructions, rules, and safety warnings
The Zero Conditional is very common in manuals, recipes, safety guidelines, and official rules. The result clause often uses an imperative (a command) rather than a present simple statement. This structure tells the reader exactly what to do when the condition occurs.
- If the alarm sounds, exit the building by the nearest emergency door.
- If the dough feels sticky, add a little more flour.
- If a passenger feels unwell, press the call button above your seat.
Definitions and explanations
We also use the Zero Conditional to give definitions — to explain what something is or what a word means by describing the condition under which it applies. This is especially useful in academic and technical writing.
- If a substance dissolves in water, it is soluble.
- If a triangle has three equal sides, it is an equilateral triangle.
- If a person is under 18, they are legally a minor in most countries.
Signal Words and Conjunctions
Zero Conditional vs First Conditional
This is the most common confusion at B1 level. Both structures use an if-clause, but they express very different things.
Zero Conditional — always true
If you heat water to 100°C, it boils.
This is a law of physics — it is always true, everywhere, for everyone. Both verbs are in the Present Simple. There is no uncertainty.
First Conditional — possible future
If you heat the soup, I will eat it.
This is a specific promise about one future occasion. The result is possible but not guaranteed. The main clause uses will.
Zero Conditional — general habit
If I drink coffee late, I can't sleep.
This is a personal truth that happens every time — a reliable pattern in the speaker's life. The Present Simple in both clauses signals a consistent rule.
First Conditional — specific prediction
If I drink coffee tonight, I won't sleep.
This is a prediction about tonight specifically — a particular consequence on a particular occasion. Won't marks it as First Conditional.
Quick test: "Is this true for everyone, always?" → Zero Conditional. "Is this about one specific future situation?" → First Conditional. The presence of will / won't in the result clause is the clearest sign you need the First, not the Zero.
IF vs WHEN in the Zero Conditional
One of the most useful features of the Zero Conditional is that if and when are often interchangeable. But there is a subtle difference in meaning worth knowing.
IF — the condition may or may not occur
If you mix these chemicals, they react.
If introduces a condition that might happen. You are describing what the result would be, but you are not assuming the condition will definitely occur.
WHEN — the condition will definitely occur
When you mix these chemicals, they react.
When implies the condition is expected to occur. We often use when in instructions because we assume the reader will carry out the action.
Common Mistakes
Using "will" in the if-clause
✗ If water will freeze, it becomes ice.
✓ If water freezes, it becomes ice.
In the Zero Conditional, the if-clause uses the Present Simple — never will. We never use will in the if-clause of any conditional. This is the single most common conditional error for B1 learners. Think of both clauses as simply present tense facts.
Using Zero Conditional for a specific future situation
✗ If it rains tomorrow, I stay at home.
✓ If it rains tomorrow, I will stay at home.
Tomorrow refers to one specific future occasion — not a universal truth. When the result is a specific future consequence rather than a guaranteed fact, use the First Conditional with will in the main clause.
Forgetting the comma when the if-clause comes first
✗ If you heat ice it melts.
✓ If you heat ice, it melts.
When the if-clause comes first, a comma separates it from the main clause. This applies to all conditional types. When the main clause comes first, no comma is needed: "Ice melts if you heat it."
Double negative with "unless"
✗ Plants die unless you water them not.
✓ Plants die unless you water them.
Unless already means "if … not", so adding not after it creates a double negative. Say either "Plants die unless you water them" or "Plants die if you don't water them" — never both.
Using past tense for universal facts
✗ If you dropped something, it fell.
✓ If you drop something, it falls.
Universal truths are not limited to the past — they are true now and always. The Zero Conditional uses Present Simple in both clauses because the fact it describes is permanently true.
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