English conditional sentences
Prototypical conditional sentences in English are those of the form "If X, then Y". The clause X is referred to as the antecedent, while the clause Y is called the consequent. A conditional is understood as expressing its consequent under the temporary hypothetical assumption of its antecedent.
Conditional sentences can take numerous forms. The consequent can precede the "if"-clause and the word "if" itself may be omitted or replaced with a different complementizer. The consequent can be a declarative, an interrogative, or an imperative. Special tense morphology can be used to form a counterfactual conditional. Some linguists have argued that other superficially distinct grammatical structures such as wish reports have the same underlying structure as conditionals.
Conditionals are one of the most widely studied phenomena in formal semantics, and have also been discussed widely in philosophy of language, computer science, decision theory, among other fields.
Overview
In English conditional sentences, the antecedent is a dependent clause, most commonly introduced by the complementizer if. Other complementizers may also be used, such as whenever, unless, provided , and as long as. Certain condition clauses can also be formulated using [|inversion] without any conjunction; see [|below].The consequent clause, expressing the consequence of the stated condition, is generally a main clause. It can be a declarative, interrogative, or imperative clause. It may appear before or after the condition clause:
As with other dependent clauses in written English, it is for a comma to be used to separate the clauses if the dependent clause comes first. See.
It is possible for the consequence clause to appear alone in a sentence, without a condition clause, if the condition has been previously stated or is understood from the context. It may also be shortened by verb phrase ellipsis; a minimal conditional sentence could therefore be something like "Would you?" or "I would." This phenomenon is known as modal subordination.
Counterfactual conditionals
Like other languages, English uses past tense morphology to indicate that the speaker regards the antecedent as impossible or unlikely. This use of past tense is often referred to as fake past since it does not contribute its ordinary temporal meaning. Conditionals with fake past marking go by various names including counterfactuals, subjunctives, and X-marked conditionals.In older dialects and more formal registers, the form "were" is often used instead of "was". Counterfactuals of this sort are sometimes referred to as were'd up conditionals.
The form "were" can also be used with an infinitive to form a future less vivid conditional.
Counterfactuals can also use the pluperfect instead of the past tense.
English language teaching
In English language teaching, conditional sentences are often classified under the headings zero conditional, first conditional, second conditional, third conditional and mixed conditional, according to the grammatical pattern followed, particularly in terms of the verb tenses and auxiliaries used.Zero conditional
"Zero conditional" refers to conditional sentences that express a factual implication, rather than describing a hypothetical situation or potential future circumstance. The term is used particularly when both clauses are in the present tense; however such sentences can be formulated with a variety of tenses/moods, as appropriate to the situation:The first of these sentences is a basic zero conditional with both clauses in the present tense. The fourth is an example of the use of will in a condition clause. The use of verb tenses, moods and aspects in the parts of such sentences follows general principles, as described in Uses of English verb forms.
Occasionally, mainly in a formal and somewhat archaic style, a subjunctive is used in the zero-conditional condition clause. For more details see English subjunctive.
First conditional
"First conditional" or "conditional I" refers to a pattern used in predictive conditional sentences, i.e. those that concern consequences of a probable future event. In the basic first conditional pattern, the condition is expressed using the present tense, and the consequence using the future construction with will :The use of present tense in dependent clauses with future time reference is not confined to condition clauses; it also occurs in various temporal and relative clauses, as described under.
The present tense used in the condition clause may take the form of the simple present as in the above examples, or the present progressive, present perfect or present perfect progressive as appropriate :
The condition can also be expressed using the modal verb should. This form can be used to make an [|inverted condition clause] without a conjunction:
Otherwise, the condition clause in a first conditional pattern is not normally formed with a modal verb, other than can. However, there are certain situations where will, would and could may be used in such clauses; see below. For the occasional use of the subjunctive in the condition clause, see under zero conditional above. In colloquial English, an imperative may be used with the meaning of a condition clause, as in "go eastwards a mile and you'll see it".
Although the consequence in first conditional sentences is usually expressed using the will future, other variations are also possible – it may take the form of an imperative, it may use another modal verb that can have future meaning, or it may be expressed as a deduction about present or past time :
A particular case involves a condition clause that expresses a goal, and the main clause expresses something that is necessary for the achievement of that goal, usually using a modal verb of necessity or obligation. In this case it is effectively the main clause, rather than the dependent condition clause, that expresses a "condition".
As noted in the following section, it may be possible to express a statement about a hypothetical future situation using either the first or second conditional pattern, with little specific difference in meaning.
Second conditional
"Second conditional" or "conditional II" refers to a pattern used to describe hypothetical, typically counterfactual situations with a present or future time frame. 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:The past tense of the condition clause is historically the past subjunctive. In modern English this is identical to the past indicative, except in the first and third persons singular of the verb be, where the indicative is was and the subjunctive were; was is sometimes used as a colloquialism, although the phrase if I were you is common in colloquial language. For more details see.
When were is the verb of the condition clause, it can be used to make an inverted condition clause without a conjunction. If the condition clause uses the past tense of another verb, it may be replaced by the auxiliary construction were to + infinitive ; if this is done, then inversion can be applied here too:
Another possible pattern is if it weren't for..., which means something like "in the absence of...". For clauses with if only, see.
For the possible use of would or could in the condition clause as well, see below.
The conditional construction of the main clause is usually the simple conditional; sometimes the conditional progressive is used. Occasionally, with a first person subject, the auxiliary would is replaced by should. Also, would may be replaced by another appropriate modal: could, should, might.
When referring to hypothetical future circumstance, there may be little difference in meaning between the first and second conditional. The following two sentences have similar meaning, although the second implies less likelihood that the condition will be fulfilled:
Notice that in indirect speech reported in the past tense, the first conditional naturally changes to the second:
Third conditional
"Third conditional" or "conditional III" is a pattern used to refer to hypothetical situations in a past time frame, generally counterfactual. Here the condition clause is in the past perfect, and the consequence is expressed using the conditional perfect.It is possible for the usual auxiliary construction to be replaced with were to have + past participle. That used, the above examples can be written as such:
The condition clause can undergo inversion, with omission of the conjunction:
Another possible pattern is if it hadn't been for..., which means something like "in the absence of...", with past reference. For clauses with if only, see.
For the possible use of would in the condition clause, see. Occasionally, with a first person subject, would is replaced with should. In the main clause, the auxiliary would can be replaced by could or might, as described for the second conditional.
If only one of the two clauses has past reference, a mixed conditional pattern is used.
Mixed conditional
"Mixed conditional" usually refers to a mixture of the second and third conditionals. Here either the condition or the consequence, but not both, has a past time reference.When the condition refers to the past, but the consequence to the present, the condition clause is in the past perfect, while the main clause is in the conditional mood as in the second conditional.
When the consequence refers to the past, but the condition is not expressed as being limited to the past, the condition clause is expressed as in the second conditional, while the main clause is in the conditional perfect as in the third conditional:
Other variations on the respective clause patterns are possible, as used accordingly in the second and third conditionals.