A conditional sentence describes a situation (the condition) and what follows from it (the result). It lets you talk about what happens when something is true, what will happen if something occurs, what would happen in an imagined world, and what would have happened in a different past.
Most conditional sentences are built around the word if, which is why they are often called if-clauses.
The two-clause structure
Every conditional has two parts: the if-clause sets the condition, and the main clause gives the result.
The condition is the situation being considered. The result is what follows from that situation. Neither clause can stand alone as a full conditional idea — they depend on each other.
The four main types
English has four standard conditional patterns. Each one describes a different kind of condition: a general truth, a real future possibility, an imagined present, or an unreal past. Each type has its own lesson; the table below is just a preview.
| TYPE | USE | EXAMPLE |
|---|---|---|
| Zero | General truths and facts | If you heat water, it boils. |
| First | Real, likely future | If it rains tomorrow, we'll stay in. |
| Second | Hypothetical present or future | If I had more time, I would learn Japanese. |
| Third | Unreal past | If Daniel had left earlier, he would have caught the train. |
The difference between them is carried by the verb forms, not by the word if. Choosing the right pattern is the main skill of working with conditionals, and each pattern is covered in the lessons that follow.
Order of clauses
The if-clause can come first or second. The meaning stays the same.
The only difference is punctuation. When the if-clause comes first, put a comma between the two clauses. When it comes second, no comma is needed.
Other words that introduce a condition
If is the default, but it is not the only option. A few other words work in a similar way — unless (meaning if not), when, as long as, provided that. These alternatives have their own lesson and are covered separately.
Common mistakes
Missing the comma after a front if-clause
Adding a comma when the if-clause comes second
Treating the if-clause as a full sentence
Confusing condition and result