English Conditionals

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.

First Conditional:

 "First conditional" or "conditional I" refers to a pattern used in predictive conditional sentences, i.e. those that concern consequences of a possible future event.

If you make a mistake, someone will let you know
If he asks me, I will consider his proposal carefully.

Second Conditional:

"Second conditional" or "conditional II" refers to a pattern used to describe hypothetical, typically counterfactual situations. In the normal form of the second conditional, the condition clause is in the past tense and the consequence is expressed using the conditional construction with the auxiliary would.

If I (he, she, it) was/were rich, there would be plenty of money available for this project.

If I (he, she, it) was/were speaking, you would not be allowed to interrupt like that.

 

 

Structure: If+past perfect, would+have+past participle

"Third conditional" or "conditional III" is a pattern used to refer to hypothetical situations in a past time frame, generally counterfactual (or at least presented as counterfactual, or likely to be counterfactual). Here the condition clause is in the past perfect, and the consequence is expressed using the conditional perfect.