How do “if” sentences work in English?

3 min readPublished 9 October 2026

Short answer

English “if” sentences follow a few fixed patterns, and the tense tells you how real the situation is:

Zero conditional — general truths: If you heat ice, it melts. (present + present)
First conditional — real future possibilities: If it rains, I’ll stay home. (present + will)
Second conditional — unreal or unlikely now/future: If I had more time, I’d learn Korean. (past + would)
Third conditional — unreal past, things that did not happen: If I had left earlier, I would have caught the train. (past perfect + would have)

The most important rule: no will and no would in the if part.

The patterns at a glance

Type	If-clause	Main clause	Use
Zero	present simple	present simple	facts, rules, habits
First	present simple	will + verb	likely future
Second	past simple	would + verb	imagined present or future
Third	past perfect	would have + past participle	imagined past

The two halves can swap places. When the if-clause comes first, put a comma after it: If you’re tired, go to bed. / Go to bed if you’re tired.

Zero conditional: always true

If you press this button, the machine stops.

a fact about how something works
If I drink coffee late, I can’t sleep.

a habit

When can often replace if here: When you heat ice, it melts.

First conditional: a real possibility

If you study, you’ll pass.

quite likely
If the bus is late, I’ll take a taxi.

a real plan
If you see her, tell her to call me.

imperative in the main clause

Second conditional: imagined now or in the future

The past tense here does not mean past time — it means “not real”:

If I won the lottery, I’d travel the world.

unlikely
If I lived closer, I’d visit more often.

not true now
If I were you, I’d apologise.

advice

With be, formal English uses were for all persons: If I were…, if she were…. If I was is common in speech, but If I were you is the fixed phrase.

Third conditional: imagined past

If we had known, we would have helped.

we didn’t know
She wouldn’t have missed the flight if she had left on time.

she did miss it

These often express regret or criticism: If you had told me, I could have done something.

Mixed conditionals

Sometimes the condition is in the past and the result is in the present, or the other way round:

If I had taken that job, I would be living in Berlin now.

past condition, present result
If she weren’t so busy, she would have come yesterday.

present situation, past result

Other ways to say “if”

unless = if not: I’ll go unless it rains.
as long as / provided that = only if: You can borrow it as long as you return it.
in case = as a precaution: Take an umbrella in case it rains. (not the same as if)

Common mistakes

Not: If I will see her, I will tell her.

Better: If I see her, I will tell her.
Not: If I would have known, I would have come.

Better: If I had known, I would have come.
Not: If I would be you, I would wait.

Better: If I were you, I would wait.
Not: If I had more money, I will buy a car.

Better: If I had more money, I would buy a car.
Not: If it will rain tomorrow, the match is cancelled.

Better: If it rains tomorrow, the match will be cancelled.

How to practise

Make a chain: start with If I had a free week… and continue each result as the next condition: …I’d go to the mountains. If I went to the mountains, I’d…. It is a simple way to make the second conditional automatic.

In short

Zero: present + present. First: present + will. Second: past + would. Third: past perfect + would have.
No will or would in the if-clause.
If I were you is the standard advice phrase.
Unless = if not; in case = as a precaution.

Lessons on this in the library

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