Conditionals
Zero, first, second, third and mixed conditionals, plus unless, as long as and provided that.
Conditional sentences link a condition (the if-clause) with a result (the main clause), and the verb forms must match the type of situation. The zero conditional (if + present, present) states general truths, while the first conditional (if + present, will) talks about real future possibilities. The second conditional (if + past, would) describes unreal or unlikely present situations, and the third conditional (if + past perfect, would have) talks about impossible past situations. Mixed conditionals combine a past condition with a present result (if + past perfect, would + base verb) or a present condition with a past result (if + past simple, would have + past participle). We also use 'unless' for 'if not', and 'as long as', 'provided that' and 'on condition that' to set a required condition, all followed by the present simple even with future meaning, just like 'if'. For example: 'If I were you, I would apologise' (second conditional, unreal present); 'If she had studied harder, she would be at university now' (mixed conditional, past condition with present result).
Key terms
| Type | If-clause | Main clause | Use |
|---|---|---|---|
| Zero | if + present simple | present simple | General truths and facts |
| First | if + present simple | will + base verb | Real future possibility |
| Second | if + past simple | would + base verb | Unreal or unlikely present |
| Third | if + past perfect | would have + V3 | Impossible past situation |
| Pattern | Structure | Example |
|---|---|---|
| Past condition -> present result | if + past perfect, would + base verb | If I had taken that job, I would be in London now. |
| Present condition -> past result | if + past simple, would have + V3 | If I were more careful, I wouldn't have lost my keys yesterday. |
| unless (= if not) | unless + present simple, will/won't + base verb | I won't go out unless the rain stops. |
| as long as / provided that (= only if) | as long as/provided that + present simple, will + base verb | You can borrow it as long as you return it by Friday. |
- 1Read the if-clause: The if-clause is 'If she had studied harder', which uses the past perfect (had + V3). This signals an impossible past situation, so the sentence is a third conditional.
- 2Match the main clause: A third-conditional main clause must use 'would have + past participle'. The base verb 'pass' becomes 'passed' (V3): 'would have passed'.
- 3Reject the traps: 'would pass' is second conditional (unreal present), 'will pass' is real future, and plain 'passed' has no modal. None fits the past perfect if-clause.
- 4Answer: If she had studied harder, she would have passed the exam.
- 1Identify the two time references: The if-clause 'had invested ten years ago' is about the past, but the main clause has the time word 'today', which is present.
- 2Pick the structure: A past condition with a present result uses the mixed-conditional pattern: if + past perfect, would + base verb (not 'would have + V3', which would be a past result).
- 3Reject the traps: 'would have been' wrongly keeps the result in the past; 'are' has no modal for an unreal situation; 'were' does not form a correct main clause here.
- 4Answer: If they had invested ten years ago, they would be millionaires today.
Never use 'will' or 'would' in the if-clause. The condition takes the present simple (first conditional) or the past simple (second conditional): write 'If you study', not 'If you will study'.
For the third conditional, both halves must be past: if + past perfect (had + V3) in the if-clause and 'would have + past participle' in the main clause. 'If she had studied, she would have passed' (not 'would passed' or 'would have pass').
In a mixed conditional with a present result, use 'would + base verb' (not 'would have + V3') in the main clause: 'If I had left earlier, I would be home now', not 'would have been home now'.
In the second conditional, use 'were' for all persons after 'if' (If I were you, If he were taller). 'Was' is avoided in this structure.
Rules
- 1Zero conditional: if/when + present simple, present simple (general truths). First conditional: if + present simple, will + base verb (real future).
- 2Second conditional: if + past simple, would + base verb (unreal/unlikely present); use 'were' for all persons after if.
- 3Third conditional: if + past perfect, would have + past participle (impossible past).
- 4Mixed conditionals: past condition -> present result uses 'if + past perfect, would + base verb'; present condition -> past result uses 'if + past simple, would have + past participle'.
- 5Use 'unless' for 'if not', and 'as long as / provided that / on condition that' + present simple (even for future meaning) to set a required condition.
Practice
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