Conditional sentences express relationships between a condition and its consequence. They are typically built from an if-clause (protasis) and a result clause (apodosis), though other markers (unless, provided that, as long as, supposing) also introduce conditions.
ELT conventionally teaches four (or five) conditional types:
| Type | Condition | Form | Example |
|---|---|---|---|
| Zero | General truth / habit | If + present, present | If you heat water to 100°C, it boils. |
| First | Real / possible future | If + present, will + base | If it rains, I'll stay home. |
| Second | Unreal / hypothetical present | If + past, would + base | If I had more time, I'd learn Japanese. |
| Third | Unreal / counterfactual past | If + past perfect, would have + pp | If she had studied, she would have passed. |
| Mixed | Past condition → present result (or vice versa) | Various combinations | If I had taken that job, I'd be in London now. |
Authentic English conditionals are far more fluid than the four-type model suggests:
The rigid type classification can lead learners to produce grammatically correct but pragmatically odd sentences, or to assume that mixing forms is always an error.
The use of past tense in second and third conditionals is a key illustration of the Tense Aspect and Time distinction: the past form signals remoteness from reality, not past time. If I were rich is about now, not then. This "modal past" or "hypothetical past" is one of the hardest concepts for L2 learners because it violates the assumed tense-time correspondence.