The Zero Conditional in English (A2)
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The zero conditional (If + present simple, present simple) describes facts and results that are always true. This lesson shows how to use it for science, rules and general truths.
The zero conditional describes things that are always true. If you heat water to 100 degrees, it boils. There is nothing hypothetical about it — the result follows from the condition every single time, which is why this structure is used for scientific facts, general truths and fixed rules.
The form is the simplest of all the conditionals: present simple in both halves. If plus present simple, then present simple. No will, no would, no past tense anywhere. This makes it the natural starting point before moving on to the first and second conditionals.
A useful signal is that you can almost always replace if with when without changing the meaning. If it rains, the streets flood and When it rains, the streets flood say the same thing, because the condition is not in doubt — it is simply a matter of time. In the first conditional this substitution does not work, which makes it a reliable test.
How to form The Zero Conditional
| Part | Form | Example |
|---|---|---|
| Condition | if + present simple | If you press this button, |
| Result | present simple | the machine stops. |
| Reversed order | result + if + condition | The machine stops if you press this button. |
| With when | when + present simple | When you press this button, the machine stops. |
| Negative condition | if + don't/doesn't | If you don't water plants, they die. |
| Imperative result | if + present, imperative | If the alarm sounds, leave the building. |
The Zero Conditional: the key rules
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Form: If + present simple, present simple — for things that are always true.
If you heat ice, it melts.
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Use it for scientific facts, rules and habits.
If I drink coffee after 6, I don't sleep.
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When can replace if with no change of meaning.
When it rains, the match is cancelled.
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The if-clause can come second, with no comma.
Plants die if they don't get water.
When to use The Zero Conditional
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Scientific and general facts
Things that are universally true, which is the classic textbook use.
If you mix red and blue, you get purple.
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Rules and routines
Fixed procedures at work, at home or in an institution.
If a customer complains, we offer a refund.
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Instructions with an imperative
A very common practical pattern where the result clause is a command.
If the light turns red, stop immediately.
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Personal habits
What you always do in a given situation — technically a general truth about yourself.
If I drink coffee late, I can't sleep.
Zero conditional vs. first conditional
The zero conditional describes what always happens; the first describes what will happen on one specific future occasion.
Zero — always true
Present simple in both halves. If can be swapped for when with no change in meaning.
If it rains, the ground gets wet. (every time)
First — one future possibility
Present simple in the if clause, will in the result. Refers to a specific occasion that may or may not happen.
If it rains tomorrow, we will stay in. (this one time)
The Zero Conditional in example sentences
- If you freeze water, it turns to ice.A scientific fact — always true.
- Plants die if they don't get light.Reversed order, no comma needed.
- If I eat late, I sleep badly.A personal general truth.
- When you heat metal, it expands.when works identically to if here.
- If the phone rings, don't answer it.Imperative in the result clause.
- The alarm goes off if someone opens the door.A fixed rule about how a system behaves.
- If you don't pay on time, the service stops.Negative condition with a factual result.
- Ice melts if you leave it in the sun.General truth in reversed order.
The Zero Conditional in a real conversation
Every conditional here describes something that happens reliably, not a one-off possibility.
Technician:If the red light flashes, the machine needs water.
Trainee:And if I ignore it?
Technician:It shuts down automatically if the tank is empty.
Trainee:What happens when the filter gets blocked?
Technician:The pressure drops. If that happens, you call maintenance.
Trainee:So if I follow the checklist, nothing goes wrong.
Common mistakes (and how to fix them)
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If you will heat water to 100°C, it boils.
If you heat water to 100°C, it boils.
The zero conditional uses present simple in both halves — no will.
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If she eat too much sugar, she feels sick.
If she eats too much sugar, she feels sick.
Present simple still needs its third-person -s inside the if-clause.
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When I'll see him, I say hello.
When I see him, I say hello.
After if/when in conditionals, will is banned.
Check yourself: 10 The Zero Conditional questions
Answer these and see the reason for each one. They are 10 of the 60 exercises in the full The Zero Conditional practice set.
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If you heat ice, it ___.
- will melt
- melted
- melts
- is melting
Show answer
melts — Both halves of a zero conditional are in the present simple.
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If the light ___ red, stop.
- will turn
- turned
- is turn
- turns
Show answer
turns — An instruction uses the present simple in the if clause.
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If you press this button, the machine ___.
- starts
- is starting
- will start
- started
Show answer
starts — Both clauses stay in the present simple.
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If I ___ late, my boss says nothing.
- am arriving
- arrive
- will arrive
- arrived
Show answer
arrive — A repeated situation takes the present simple.
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She gets a headache if she ___ enough sleep.
- didn't have
- isn't having
- doesn't have
- won't have
Show answer
doesn't have — The negative present simple is used for a repeated condition.
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Ice ___ if you leave it in the sun.
- melted
- is melting
- will melt
- melts
Show answer
melts — A general truth takes the present simple in both halves.
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If you heat water to a hundred degrees, it ___.
Show answer
boils — A scientific fact takes the present simple in both clauses.
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Metal expands ___ you heat it.
Show answer
if — If and when are interchangeable when the result is always true.
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If you mix red and white, you ___ pink.
Show answer
get — A fact that is always true takes the present simple.
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If the temperature ___ below zero, the pipes freeze.
Show answer
falls — Both clauses are present simple in a zero conditional.
Practise The Zero Conditional today
Test each sentence with the when substitution — it confirms you have the zero conditional.
- Write four scientific facts using the zero conditional.
- Write four rules from your workplace, school or home in the same structure.
- Rewrite each one with when instead of if and check the meaning is unchanged.
- Write three instructions where the result clause is an imperative.
The Zero Conditional: frequently asked questions
What is the difference between if and when in the zero conditional?
Essentially nothing, which is the defining feature of this structure. Because the result follows the condition every time, whether you frame it as if or when makes no practical difference. This is the clearest test for identifying a zero conditional: if swapping if for when changes the meaning or sounds odd, you are looking at a first conditional instead.
Do I need a comma?
Only when the if clause comes first: If you heat water, it boils. When the result clause comes first, no comma is used: Water boils if you heat it. This rule applies to all conditional types in English, and it is worth applying consistently because it is checked in written exams.
Can I use will in the zero conditional?
No. Will introduces a specific future occasion, which shifts the sentence into the first conditional. If you heat water, it will boil is grammatically fine but it now describes one particular pot of water rather than a general law. For universal truths, keep both halves in the present simple.
Is the zero conditional only for science?
Not at all — that is just the clearest textbook illustration. It is used constantly for workplace procedures, machine behaviour, household rules and personal habits: If I skip breakfast, I get a headache. Anything that reliably produces the same result belongs here, which makes it far more common in everyday speech than its name suggests.