A conditional relates to a sentence that expresses a condition. A conditional sentence is made up of two clauses, the first of which is the conditional clause and it starts with if, unless, when, etc. Most commonly, it starts with if and we refer to it as the if-clause (or if clause or ‘if’ clause). The if-clause contains a condition, which if fulfilled another action will take place.
The other clause of the conditional sentence is the main clause (or result clause). The main clause shows the effect of the action taken or if taken in the if-clause. The if-clause usually comes before the main clause although the reverse is possible. A comma comes after the if-clause if the clause comes before the main clause, but if the main clause comes earlier, no comma is required.
An example should make it clear:
You enter at your own risk if the building is unsafe.
*This conditional uses the simple present tense in both parts of the sentence and is described as the fourth type known as the ‘zero’ conditional.
There are three main types of conditional. They are commonly referred to as the First Conditional, the Second Conditional, and the Third Conditional. (or simply, Type 1, Type 2 or Type 3 Conditionals.)
Each of these is explained further in the following sections: