The four conditionals at a glance
A conditional sentence has two parts: an if-clause (the condition) and a result clause. English has four basic patterns. Two describe real conditions — things that are true or genuinely possible. Two describe unreal conditions — imaginary situations.
| Conditional | Structure | Meaning |
|---|
| Zero | if + simple present, ... simple present | a general truth |
| First | if + simple present, ... will + base verb | a future possibility |
| Second | if + simple past, ... would + base verb | a hypothetical present |
| Third | if + past perfect, ... would have + past participle | a hypothetical past |
The golden rule: never put will or would in the if-clause. The tense in the if-clause always steps one step "back" from the tense in the result.
Real conditions · Zero and First
The zero conditional states a general truth, a scientific fact or an automatic result. Both clauses use the simple present, and you can replace if with when without changing the meaning.
If / When + simple present, ... simple present
If you heat ice, it melts.
If the hypothesis isn't correct, the scientists form a new one.
Metal expands if you warm it.
The first conditional talks about a real possibility in the future. The if-clause stays in the present even though it refers to the future; only the result clause takes will.
If + simple present, ... will + base verb
If you carry out this experiment, you will see some interesting results.
If you have the right expertise, you will make the most of your luck.
What will you do if the funding doesn't arrive?
Tip: unless means if ... not: Unless the results are clear, we repeat the test. = If the results aren't clear, we repeat the test. You can also swap will for may, might, can or an imperative in the result clause.
Unreal conditions · Second and Third
The second conditional imagines a present or future situation that is not true — it's improbable, impossible, or simply hypothetical. The past tense here does not refer to past time; it signals distance from reality.
If + simple past, ... would + base verb
If I were a scientist, I would like to work in a research lab.
The world would be a very different place if we didn't have them.
If we had more funding, we would hire two more researchers.
The third conditional imagines a different past. The events are finished and cannot be changed, so we often use it to express regret, criticism or relief.
If + past perfect, ... would (not) have + past participle
If they hadn't spent years in their laboratories, they wouldn't have had the expertise they needed.
If I had been in Alexander Fleming's position, I would not have noticed the same thing he did.
Would penicillin have been discovered if that dish hadn't been left out?
Note: after if, were is used for every person in careful English: If he were here... Also watch the contraction 'd: in If I'd known it is had, but in I'd tell you it is would.
Word order and punctuation
Either clause can come first. When the if-clause comes first, separate the two clauses with a comma. When the result clause comes first, use no comma.
If you heat ice, it melts.
Ice melts if you heat it.
⚠ Common mistakes:
✗ If it will rain, we will cancel. → ✓ If it rains, we will cancel. (no will in the if-clause)
✗ If I would have known, I would have told you. → ✓ If I had known, I would have told you.
✗ If she studies medicine, she will works in a hospital. → ✓ she will work (base verb after will)
✗ He wouldn't discovered penicillin. → ✓ He wouldn't have discovered penicillin.
✗ If we didn't had them... → ✓ If we didn't have them...