A conditional sentence describes a condition and its result: if one thing happens (or happened, or were true), then another thing follows. Every conditional has two parts — the if-clause (the condition) and the main clause (the result).
English has four main types — zero, first, second and third — plus mixed conditionals. The type you choose depends on two questions: when is the situation (general, future, present, past)? and how real is it (true, likely, imaginary, impossible)? It does not depend on how the sentence would be translated from your first language.
The conditional types at a glance
| Type | If-clause | Main clause | Use | Example |
|---|---|---|---|---|
| Zero | present simple | present simple | Facts, general truths, habits | If you heat ice, it melts. |
| First | present simple | will + base verb | Real, likely future | If it rains, we will stay in. |
| Second | past simple | would + base verb | Imaginary or unlikely present/future | If I had a car, I would drive. |
| Third | past perfect | would have + past participle | Imaginary past (it didn't happen) | If I had left early, I would have caught the train. |
| Mixed | past perfect | would + base verb | Past condition → present result | If I had studied medicine, I would be a doctor now. |
Zero conditional: facts and general truths
Use the zero conditional for things that are always true when the condition is met — scientific facts, rules, habits and instructions. Because the result always follows, you can replace if with when without changing the meaning.
- If you heat water to 100°C, it boils.
- If I drink coffee after 6 p.m., I can't sleep.
- If the light is red, cars stop.
- If you mix blue and yellow, you get green.
- Plants die if they don't get enough water.
Instructions often use an imperative in the main clause: If you feel dizzy, sit down. / If the alarm sounds, leave the building.
First conditional: real future possibilities
Use the first conditional when the situation is possible and realistic in the future, and you are thinking about its likely result. Promises, warnings, threats and plans often use this form.
- If it rains tomorrow, we will stay at home.
- If you study every day, you will pass the exam.
- If she doesn't hurry, she will miss the bus.
- I'll call you if I finish early.
- If you touch that wire, you'll get a shock. (warning)
Variations. The main clause can use other modals instead of will to change the certainty: If you leave now, you might catch the train (possible) · If you finish your work, you can go home (permission) · If you feel ill, you should see a doctor (advice). See our modal verbs guide for the full range.
Second conditional: imaginary present and unlikely future
The second conditional is for situations that are not true now or unlikely to happen. The past tense in the if-clause does not refer to past time — it signals distance from reality.
- If I had more time, I would learn Japanese. (I don't have time.)
- If I won the lottery, I would buy a house by the sea. (unlikely)
- If she lived closer, we would see her more often.
- What would you do if you lost your job?
- If I were you, I would apologise. (advice)
"If I were" vs. "If I was". In formal and exam English, use were for every subject in the second conditional: If I were rich… / If he were taller…. Was is common in relaxed speech, but If I were you is the fixed phrase for giving advice.
First or second? The choice shows how likely you think the situation is. If I get the job, I'll move to London (I have a real chance) vs. If I got the job, I'd move to London (I doubt I'll get it).
Third conditional: imaginary past
The third conditional imagines a different past — something that did not happen — and its imaginary result. It is used for regret, criticism, relief and reflection. Because the past cannot change, the situation is always impossible.
- If I had studied harder, I would have passed. (I didn't study; I failed.)
- If she had left earlier, she wouldn't have missed the flight.
- If we hadn't taken a taxi, we would have been late. (relief)
- If you had told me, I would have helped you.
- He could have won if he had trained more. (could have = would have been able to)
In speech, had and would both contract to 'd: If I'd known, I'd have come. The first 'd = had; the second 'd = would.
Mixed conditionals
Mixed conditionals combine two different time frames. They are less frequent, but they appear in advanced writing, IELTS essays and natural speech.
Past condition → present result
- If I had taken that job, I would be living in Canada now.
- If she hadn't missed the bus, she would be here.
Present condition → past result
- If I spoke French, I would have understood the film. (I don't speak French — so I didn't understand it.)
- If he weren't so shy, he would have asked her to dance.
Unless, in case, provided that and other conditional words
| Word / phrase | Meaning | Example |
|---|---|---|
| unless | if … not / except if | You won't improve unless you practise. (= if you don't practise) |
| as long as / provided (that) / providing | only if (a condition you insist on) | You can borrow the car as long as you drive carefully. |
| in case | as a precaution — not the same as "if" | Take an umbrella in case it rains. (take it now, before you know) |
| otherwise | if not, then… | Hurry up, otherwise we'll be late. |
| suppose / supposing / imagine | introduces an imaginary condition | Suppose you lost your passport — what would you do? |
| even if | the result doesn't change | Even if it rains, we'll go. |
Inversion (formal English)
In formal writing, if can be dropped and the auxiliary moved to the front: Had I known (= If I had known), Were I in your position (= If I were…), Should you need help (= If you need help). This is useful for C1–C2 writing and formal emails.
Clause order and the comma
The if-clause can come first or second. The meaning doesn't change, but the punctuation does:
- If-clause first → use a comma: If you need help, call me.
- Main clause first → no comma: Call me if you need help.
Common mistakes with conditionals
| ✗ Incorrect | ✓ Correct | Why |
|---|---|---|
| If it will rain, we will stay home. | If it rains, we will stay home. | No will in the if-clause of a first conditional. |
| If I would have money, I would travel. | If I had money, I would travel. | Would belongs in the main clause only. |
| If I would have known, I would have come. | If I had known, I would have come. | Third conditional uses had + past participle in the if-clause. |
| If I knew, I would have told you. | If I had known, I would have told you. | Both halves are about the past → third conditional. |
| Unless you don't study, you'll fail. | Unless you study, you'll fail. | Unless already means "if not". |
| Take a coat if it gets cold. (meaning precaution) | Take a coat in case it gets cold. | In case = do it now as a precaution. |
How to choose the right conditional — a 3-step check
- Is it always true? → zero conditional.
- Is it about the past? → third conditional (or mixed, if the result is in the present).
- Is it about now or the future? If it's realistic → first conditional. If it's imaginary or unlikely → second conditional.
Practice exercise
Complete each sentence with the correct form of the verb in brackets.
- If you ______ (freeze) water, it turns to ice.
- If she ______ (call), I'll tell her the news.
- If I ______ (be) you, I would take the job.
- If they had booked earlier, they ______ (get) cheaper tickets.
- We'll miss the start of the film unless we ______ (leave) now.
- If he ______ (not / lose) his phone, he wouldn't have been late.
- If I had more money, I ______ (buy) a new laptop.
- If I had gone to bed earlier last night, I ______ (not / be) so tired now.
- Take some water in ______ you get thirsty.
- If you ______ (need) anything, just ask.
Show answers
- freeze (zero)
- calls (first)
- were (second — "If I were you")
- would have got / would have gotten (third)
- leave (unless + present)
- hadn't lost (third)
- would buy (second)
- wouldn't be (mixed: past condition → present result)
- case (in case = precaution)
- need (first / zero — both acceptable)
Where to go next
Conditionals depend on solid tense control, so review the past perfect (for third conditionals) and the full tense chart. In exams, second and third conditionals help you discuss hypothetical situations in IELTS Writing Task 2. When you report what someone said about a condition, the rules of reported speech apply. Test yourself with the Grammar Quiz.
Frequently asked questions
What is a conditional sentence?
A conditional sentence has two parts: an if-clause that states a condition and a main clause that states the result. For example, in “If it rains, we will stay home,” the condition is “if it rains” and the result is “we will stay home.”
How many types of conditional sentences are there?
English has four main types — zero, first, second and third conditional — plus mixed conditionals that combine two time frames. The zero and first describe real situations; the second and third describe imaginary ones.
Can we use “will” in the if-clause?
Not in a normal first conditional: say “If it rains, we will stay home,” not “If it will rain.” The exception is when “will” means willingness or a polite request, as in “If you will wait here, I’ll get the manager.”
Is it “If I was” or “If I were”?
In the second conditional, “If I were” is the correct form in formal and exam English, and it is fixed in the advice phrase “If I were you.” “If I was” is common in casual speech.
What is the difference between “unless” and “if not”?
“Unless” usually means “if not” or “except if”: “You’ll be late unless you hurry” = “You’ll be late if you don’t hurry.” Don’t add another “not” after “unless”.
Do I need a comma in a conditional sentence?
Use a comma when the if-clause comes first (“If you need help, call me”). No comma is needed when the main clause comes first (“Call me if you need help”).