Conditional Sentences in English: Zero, First, Second and Third

A conditional sentence has two parts: a condition (usually starting with if) and a result. If it rains, we'll stay at home. English has four main types, traditionally numbered zero to three, and the choice between them depends on one question: is the situation real, possible or imagined — and is it about the present, the future or the past?

Here's each type, how to form it, and how to choose.

The four types at a glance

Zero conditional: facts

If + present simple, present simple. For things that are always true — science, rules, habits. If means almost the same as when or whenever.

First conditional: real possibilities

If + present simple, will + verb. For a situation that could really happen in the future, and its likely result.

A very common mistake happens here: no will in the if-clause, even though it's about the future.

(There are exceptions — polite requests like If you'll wait here a moment, I'll get the manager — but in ordinary conditions, leave will out.)

The result can also use can, may, might or an instruction: If you finish early, you can go home. If you see Tom, tell him to call me.

Second conditional: imagined situations

If + past simple, would + verb. For situations that aren't true now, or are unlikely in the future. The past form doesn't mean past time — it signals "imagined".

With be, use were for every person in careful English — especially in the fixed phrase for advice:

(If I was is common in informal speech, but If I were you is the standard form and the safe choice in exams.)

First or second? It depends how likely it is

The same idea can be first or second conditional — the choice shows what you think:

Third conditional: the past that didn't happen

If + past perfect, would have + past participle. For imagining a different past — often regrets, criticism or relief.

In speech, would have usually sounds like would've /ˈwʊdəv/ — and if you'd here means if you had. If the past perfect is new to you, start with how the past perfect works.

Mixed conditionals

Sometimes the condition and the result are at different times. The most common mix: an imagined past condition with a present result.

Other words for "if"

• unless = if … not: I won't go unless you come too. (= if you don't come)
• as long as / provided that = only if: You can borrow the car as long as you're careful.
• when — for things you're sure will happen: When I get home, I'll call you. (Compare If I get home before ten… — not sure.)
• in case — not the same as if! It means "as a precaution": Take an umbrella in case it rains. (Take it now, because it might rain.)

Common mistakes

• Will in the if-clause: If it will rain, we'll stay in. → If it rains, we'll stay in.
• Would in the if-clause: If I would have more money, I'd travel. → If I had more money, I'd travel.
• Mixing up second and third: If I knew yesterday, I would have come. → If I had known, I would have come.
• "Would have" with the wrong verb form: I would have went. → I would have gone.
• "Would of": it sounds the same as would've, but in writing it's always would have.

How to get comfortable with conditionals

Conditionals are easiest to learn by using them about your own life. Each day, say three sentences out loud: one first conditional about tomorrow (If I finish work early, I'll…), one second conditional about a dream (If I could live anywhere, I'd…), one third conditional about the past (If I hadn't…, I wouldn't have…). Speaking them, not just reading them, is what makes them automatic — the same principle behind practising speaking on your own.

Quick check

Put the verbs in the correct form. Answers are below.

1. If you ___ (mix) red and blue, you get purple.
2. If it ___ (be) sunny tomorrow, we ___ (go) to the beach.
3. If I ___ (be) you, I ___ (not / sign) that contract.
4. If she ___ (study) harder, she ___ (pass) the exam last year.
5. I'll be in meetings all day, so I won't call you ___ there's an emergency. (if / unless)