English conditional sentences

As is typical for many languages, full conditional sentences in English consist of a condition clause or protasis specifying a condition or hypothesis, and a consequence clause or apodosis specifying what follows from that condition. The condition clause is a dependent clause, most commonly headed by the conjunction if, while the consequence is contained in the main clause of the sentence. Either clause may appear first.

Different types of conditional sentences (depending largely on whether they refer to a past, present or future time frame) require the use of particular verb forms (tenses and moods) to express the condition and the consequence. In English language teaching the most common patterns are referred to as first conditional, second conditional and third conditional; there is also a zero conditional and mixed conditional.

For more general information about the uses of verb tenses, moods and aspects in English, see Uses of English verb forms.

In English conditional sentences, the condition clause (protasis) is a dependent clause, most commonly introduced by the conjunction if. Other conjunctions or equivalent expressions may also be used, such as unless (meaning "if...not"), provided (that), providing (that) and as long as. Certain condition clauses can also be formulated using inversion without any conjunction; see § Inversion in condition clauses below.

The apodosis, expressing the consequence of the stated condition, is generally the main clause of the sentence. Depending on the sentence type, it may be a statement, question, or order. It may appear before or after the condition clause:

...
Wikipedia