Zero Conditional Rules

The zero conditional is one of the simplest yet most powerful structures in English. We use it to talk about things that are always true—scientific facts, natural laws, and universal truths. If you want to sound confident and accurate when discussing facts, this is the conditional you need to master.

What is the Zero Conditional?

The zero conditional describes situations where one thing always leads to another. There's no doubt, no maybe—it's a certainty. When the condition happens, the result always follows.

Key Insight: Unlike other conditionals that deal with possibilities or hypotheticals, the zero conditional deals with reality and certainty.

The Structure

The zero conditional has a simple, symmetrical structure:

If / When + Present Simple, Present Simple

If you heat ice, it melts.

When the sun sets, it gets dark.

Notice that both parts use the present simple tense. This reflects the timeless, factual nature of what we're describing.

Word Order Flexibility

You can reverse the order of the clauses. When the "if/when" clause comes second, you don't need a comma:

Ice melts if you heat it.

It gets dark when the sun sets.

When to Use the Zero Conditional

1. Scientific Facts

For describing natural phenomena and scientific principles:

If you mix red and blue, you get purple.

Water freezes if the temperature drops below 0°C.

If you drop something, gravity pulls it down.

Plants die if they don't get water.

2. General Truths

For things that are universally accepted as true:

If you don't eat, you get hungry.

People get tired if they don't sleep.

If you practice every day, you improve.

3. Instructions and Procedures

For explaining how things work or giving directions:

If you press this button, the machine starts.

When you click "save," the file is stored.

If you turn the key clockwise, the door opens.

4. Cause and Effect Relationships

For describing predictable outcomes:

If you touch fire, you get burned.

When it rains, the ground gets wet.

If you add salt to water, it boils at a higher temperature.

"If" vs "When" — What's the Difference?

In zero conditionals, if and when are often interchangeable, but there's a subtle difference:

If — suggests the condition may or may not happen

When — suggests the condition definitely happens (at some point)

Compare:

If it rains, the streets get wet. (Rain may or may not come)

When it rains, the streets get wet. (Rain will come eventually)

Both are grammatically correct! Choose based on what you want to emphasize.

Correct or Incorrect? Test Your Understanding

Read each statement and decide if it correctly uses the zero conditional:

1. "If water reaches 100°C, it boils."

This is a scientific fact expressed correctly with present simple in both clauses.

2. "If I will study hard, I pass the exam."

Never use "will" in the if-clause of a zero conditional. Correct: "If I study hard, I pass exams."

3. "The alarm rings when you open the door."

The order is reversed but both clauses use present simple correctly.

4. "If you would heat metal, it expands."

Don't use "would" in zero conditionals. Correct: "If you heat metal, it expands."

5. "When the sun rises, the temperature increases."

Perfect zero conditional describing a natural phenomenon.

Common Mistakes to Avoid

Mistake 1: Using "will" in the if-clause

If you will heat water, it boils.

If you heat water, it boils.

The zero conditional never uses "will" because we're describing facts, not predictions.

Mistake 2: Using "would" anywhere

If you mix yellow and blue, you would get green.

If you mix yellow and blue, you get green.

"Would" implies uncertainty or hypothetical situations—the opposite of what zero conditional expresses.

Mistake 3: Mixing tenses

If water reached 100°C, it boils.

If water reaches 100°C, it boils.

Keep both clauses in present simple for zero conditional.

Mistake 4: Using zero conditional for specific situations

If it rains tomorrow, the ground gets wet. (specific future event)

If it rains tomorrow, the ground will get wet. (first conditional)

Use zero conditional for general truths, not specific future events.

Zero Conditional vs Other Conditionals

Understanding when to use zero conditional versus other types:

Zero Conditional (100% certain, always true)

If you heat ice, it melts.

First Conditional (possible future situation)

If you heat this ice, it will melt.

Second Conditional (unlikely/hypothetical)

If you heated the ice, it would melt.

Remember: Zero conditional = facts that are ALWAYS true. First conditional = specific situations that MIGHT happen in the future.

More Examples by Category

Nature and Science

If you cool water to 0°C, it freezes.
When volcanoes erupt, they release lava.
If there is no oxygen, fire goes out.
Sound travels faster when the air is warmer.

Human Body

If you don't drink water, you become dehydrated.
When you exercise, your heart beats faster.
If you eat too much sugar, you gain weight.
Your pupils dilate when it gets dark.

Technology

If you press the power button, the computer starts.
When the battery dies, the phone turns off.
If you delete a file, it goes to the recycle bin.
The screen locks if you don't touch it for a while.

Everyday Life

If you don't set an alarm, you oversleep.
When traffic is heavy, the commute takes longer.
If you smile at people, they usually smile back.
Children learn faster when they enjoy the activity.

Quick Summary

Zero Conditional Formula:

If/When + present simple, present simple

Use it for:

Scientific facts
General truths
Instructions
Cause and effect

Never use: will, would, or past tense

Now that you understand the zero conditional, you can confidently express facts and universal truths in English. Practice by describing the world around you—what happens when certain conditions are met? The more you use this structure, the more natural it will feel!