Zero Conditional
Learn how the zero conditional uses the present simple in both clauses to describe general facts and things that are always true.
Always true, every time
The zero conditional states a result that always follows a condition.
The zero conditional is used for general facts, scientific truths and things that are always true. It follows the pattern if + present simple, present simple.
In the sentence If you heat water to 100 degrees, it boils., both clauses use the present simple, because the result is not a possibility or a guess. It happens every single time the condition is met.
This distinguishes the zero conditional from patterns such as the first conditional, where the result is a realistic possibility rather than a certainty.
Before you begin
The zero conditional is one pattern within conditionals.
This lesson focuses on the zero conditional specifically. For an introduction to conditional sentences as a whole, and how the parts of a conditional sentence are identified, begin with Understanding Conditionals.
The pattern
Both clauses use the present simple.
Compare the two parts of a zero conditional sentence.
01
The If-Clause
If + present simple.
If you heat water to 100 degrees,
02
The Main Clause
Present simple.
it boils.
Both parts of the sentence use the same tense.
Unlike the first, second and third conditionals, the zero conditional does not change tense between the two clauses, since the result always follows the condition, every time.
When is similar to if
“When” can often replace “if” without changing the meaning.
If and when
If the sun sets, it gets dark.
When the sun sets, it gets dark.
Because the relationship is a general truth rather than an uncertain condition, when can replace if in the zero conditional without changing the meaning of the sentence.
Whenever works the same way
Whenever I drink coffee late at night, I struggle to fall asleep.
Whenever can also replace if in the zero conditional, adding a sense of repetition to the general truth.
Where the zero conditional is used
The zero conditional covers facts, instructions and routines.
Scientific and natural facts
If you freeze water, it turns to ice.
Plants die if they don’t get enough light.
Instructions and rules
If the light turns red, you stop.
If a player touches the ball with their hands, the referee blows the whistle.
Here, the result is not a certainty in the scientific sense, but a fixed rule that applies every time the condition is met.
Personal habits and routines
If I wake up early, I go for a run.
The zero conditional can also describe a habit, where the result regularly follows the condition for one particular person.
A useful decision guide
Ask whether the result is a certainty or only a possibility.
01
Does the result happen every time, without exception?
Use the zero conditional: present simple, present simple.
02
Could “when” replace “if” without changing the meaning?
This is a strong sign the sentence is a zero conditional.
03
Is the result only a realistic possibility, not a certainty?
Use the first conditional instead, with will in the main clause.
Common mistakes
Do not use “will” in either clause of the zero conditional.
Using will in the main clause.
Not: If you heat water to 100 degrees, it will boil.
Correct: If you heat water to 100 degrees, it boils.
Will suggests a single future event, not a fact that is always true.
Mixing the zero and first conditional patterns.
Not: If it rains, the ground gets wet, and we will get wet too.
Correct: Choose one pattern and keep it consistent across the sentence.
Each conditional pattern keeps a consistent verb form; combining certainty and possibility in the same sentence usually means two separate ideas are being expressed at once.
Using the past simple instead of the present simple.
Not: If you heated water to 100 degrees, it boiled.
Correct: If you heat water to 100 degrees, it boils.
The zero conditional describes a fact that is true now, not something that happened once in the past.
Check your understanding
Is the zero conditional used correctly?
Choose the correct answer for each sentence.
Which sentence correctly uses the zero conditional?
✅ Exactly! Both clauses use the present simple, since this is always true.
❎ Not quite. Check whether “will” belongs in a sentence describing a fact that is always true.
The zero conditional never uses “will.”
“When the sun sets, it gets dark.” Could “when” be replaced with “if” here?
✅ Exactly! In the zero conditional, “if” and “when” are often interchangeable.
❎ Not quite. Since this is a general truth rather than an uncertain condition, “if” and “when” work the same way here.
Which sentence correctly uses the zero conditional?
✅ Exactly! This is a fixed rule, so the present simple is used in both clauses.
❎ Not quite. This describes a rule that applies every time, not a single future event.
“If I wake up early, I go for a run.” What kind of result is being described?
✅ Exactly! The zero conditional can describe habits as well as scientific facts.
❎ Not quite. Look at the verb forms; both clauses use the present simple.
Choose the best explanation
Select the sentence that explains the zero conditional correctly.
Why does “If you heat water to 100 degrees, it boils” use the present simple in both clauses?
✅ Exactly! The present simple in both clauses signals a fact that is always true.
❎ Not quite. Think about how certain this result is, compared with a first conditional sentence.
Why can “when” replace “if” in “If the sun sets, it gets dark”?
✅ Exactly! This interchangeability is specific to the zero conditional.
❎ Not quite. Think about what kind of relationship “if the sun sets, it gets dark” describes.
Why is “If you heat water to 100 degrees, it will boil” not a correct zero conditional?
✅ Exactly! The zero conditional keeps the present simple in both clauses to describe a certainty.
❎ Not quite. Compare this sentence with a first conditional sentence, where “will” is used correctly.
Try it another way
Complete each zero conditional sentence.
Type the correct form of the verb shown in brackets.
✅ Exactly! The zero conditional uses the present simple in the main clause.
❎ Not quite. Use the present simple form of “boil.”
✅ Exactly! The present simple describes a fact that is always true.
❎ Not quite. Use the present simple form of “freeze.”
✅ Exactly! This describes a fixed rule, so the present simple is used.
❎ Not quite. Use the present simple form of “stop.”
Edit the sentence
Rewrite each sentence with the correct zero conditional form.
Use the note in brackets to decide what needs to change.
If you mix red and blue, you will get purple. (correct the zero conditional)
✅ Exactly! The zero conditional replaces “will get” with the present simple “get.”
❎ Not quite. Replace “will get” with the present simple form.
If the sun sets, it gets dark. (rewrite using “when” instead of “if”)
✅ Exactly! “When” can replace “if” here without changing the meaning.
❎ Not quite. Replace “if” with “when” and keep the rest of the sentence the same.
If you don’t water the plant, it will die. (correct the zero conditional)
✅ Exactly! “Dies” replaces “will die” to match the zero conditional pattern.
❎ Not quite. Replace “will die” with the present simple form of “die.”
Quick review
The zero conditional pairs the present simple with the present simple.
The zero conditional follows the pattern if + present simple, present simple.
It describes general facts, scientific truths, fixed rules and personal habits.
When and whenever can often replace if without changing the meaning.
Will does not belong in either clause of the zero conditional.
If the result is only a realistic possibility rather than a certainty, the first conditional is used instead.
Remember
Ask whether the result is a certainty, every time.
The zero conditional is reserved for results that always follow their condition, without exception. Once that certainty is confirmed, the present simple belongs in both clauses.