Guide B2 · Upper-intermediate Grammar

Zero and First Conditionals

Understand B2 English zero and first conditionals for general truths, real possibilities, and likely results.

3 min read 504 words Updated Aug 9, 2026

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Zero and first conditionals describe real or possible situations. The key difference is whether you are describing a general result or a likely future result. Both clauses are real-world possibilities; the form shows how you connect the condition to its result.

Compare the two patterns

Conditional	Form	Example	Meaning
Zero	If + present, present	If water reaches 100°C, it boils.	A general fact or regular result.
First	If + present, will + verb	If it rains, we will stay inside.	A possible future situation.
First	Unless + present, will + verb	Unless we leave now, we will be late.	A condition that blocks the result.

Zero conditional: regular results

Use the zero conditional for facts, routines, instructions, and results that usually happen whenever the condition is true. Both clauses normally use the present simple.

Condition	Result	Meaning
If people do not sleep enough,	they feel tired.	A regular result.
If you mix blue and yellow,	you get green.	A general fact.
When the lesson ends,	the students leave.	A repeated routine.

First conditional: real future possibilities

Use the first conditional when the condition is possible and the result belongs to the future. The if-clause uses the present simple, even though it refers to the future; the result clause can use will, an imperative, or another appropriate modal.

Purpose	Example	Meaning
Prediction	If the train is late, we will take a taxi.	A possible result.
Advice or instruction	If you finish early, check your answers.	An instruction after a condition.
Possibility with a modal	If the weather improves, we might eat outside.	The result is possible, not certain.

Put the clauses in either order

The meaning stays the same when you move the if-clause. Use a comma when the if-clause comes first, but usually not when it comes second: “If I have time, I will call you” and “I will call you if I have time.”

Choose the meaning before the form

Ask whether the result is always or usually true, or whether it is a future possibility. The verb form follows that meaning; do not choose a conditional only because it sounds familiar.

Common mistakes to check

Mistake	Correction	Why
If it will rain, we will stay home.	If it rains, we will stay home.	Do not normally use will in the if-clause.
Unless you do not hurry, you will miss the bus.	Unless you hurry, you will miss the bus.	Unless already means if not.
If I finish early I will help.	If I finish early, I will help.	Use a comma after an opening if-clause.