B1 · Zero & First Conditional — Lesson

Zero conditional: general truths

The zero conditional describes facts, scientific truths, and things that are always true when the condition happens.

If + present simple, + present simple ✓

Scientific fact

If you heat water to 100°C, it boils.

General truth

If it rains, the streets get wet.

Habitual result

If I don't sleep enough, I feel terrible.

"When" can replace "if" in the zero conditional because the result is certain: When you heat water, it boils.

First conditional: real possibility

The first conditional describes a real possibility in the future — something that might genuinely happen.

If + present simple, + will + base verb ✓

Future possibility

If it rains tomorrow, I will stay home.

Warning

If you don't hurry, you will miss the bus.

Promise/offer

If you help me, I will help you.

Can/may alternative

If you come early, we can have coffee first.

Clause order: if clause first or second

Both orders are correct — comma rules change

If clause first → comma

If it rains, I will stay home.

If you study, you will pass.

Main clause first → no comma

I will stay home if it rains.

You will pass if you study.

Zero vs first: the key distinction

Zero — always true

If you mix red and blue, you get purple.

always happens

If I'm late, she gets annoyed.

always the result

First — might happen

If I'm late tomorrow, she will get annoyed.

possible future

If it rains, we will cancel the trip.

real possibility

Common mistakes

If it will rain, I will stay home.

→

If it rains, I will stay home.

if clause: present simple (NOT will)

If you will come, call me.

→

If you come, call me.

never "will" in the if-clause

If water boils, it will become steam.

→

If water boils, it becomes steam.

always-true fact → zero conditional (present both sides)

If I study, I pass the exam.

→

If I study, I will pass the exam.

specific future possibility → first conditional

Recap

Zero

If + present, + present

If water boils, it becomes steam.

First

If + present, + will + base

If it rains, I will stay home.

Key rule

NEVER "will" in the if clause

If it rains (NOT if it will rain)

Comma

if clause first → comma · main first → no comma

If it rains, I'll stay. / I'll stay if it rains.

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