Prototypical conditional sentences in English are those of the form "If X, then Y". The clause X is referred to as the antecedent (or protasis), while the clause Y is called the consequent (or apodosis). 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 (protasis) is a dependent clause, most commonly introduced by the complementizer if. Other complementizers may also be used, such as whenever, unless, provided (that), 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: If I see him, I will tell him. (declarative sentence, condition first) I will tell him if I see him. (declarative sentence, condition second) If you saw him, would you tell him? (interrogative sentence, condition first) Would you tell him if you saw him? (interrogative sentence, condition second) If you see it, photograph it. (imperative sentence, condition first) Photograph it if you see it. (imperative sentence, condition second)
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 (as is done in the above examples). 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.The term subjunctive conditional was borrowed from Latin grammar, but is a misnomer as applied to English. English conditionals of this sort do not use subjunctive mood. See Palmer (1986), Dancygier & Sweetswer (1996), Iatridou (2000), Karawani (2014), Romero (2014), Mackay (2015), von Fintel and Iatridou (2020) , among others.
Indicative: If it is raining in New York, then Mary is at home. Counterfactual: If it was raining in New York, then Mary would be at home.
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.
Were'd up: If I were king, I could have you thrown in the dungeon.
The form "were" can also be used with an infinitive to form a future less vivid conditional.
Future Less Vivid: If I were to be king, I could have you thrown in the dungeon.
Counterfactuals can also use the pluperfect instead of the past tense.
Conditional perfect: If you had called me, I would have come.
English language teaching In English language teaching, conditional sentences are often classified under the headings zero conditional, first conditional (or conditional I), second conditional (or conditional II), third conditional (or conditional III) 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 (see Types of conditional sentence). 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: If you don't eat for a long time, you become hungry. If the alarm goes off, there's a fire somewhere in the building. If you are going to sit an exam tomorrow, go to bed early tonight! If aspirins will cure it, I'll take a couple tonight. If you make a mistake, someone lets you know.
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 clauselingua.org.uk: WILL with IF (further down on the page) (for more such cases, see below). 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 (as in "If the prisoner be held for more than five days, ...). For more details see English subjunctive. (See also below.)
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 (see Types of conditional sentence). In the basic first conditional pattern, the condition is expressed using the present tense (having future meaning in this context). In some common fixed expressions or in old-fashioned or formal contexts, the present subjunctive is occasionally found. For example:If need be, we'll rent a car. see use of the present subjunctive), and the consequence using the future construction with will (or shall): If you make a mistake, someone will let you know. If he asks me, I will/shall consider his proposal carefully.
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 soon as he arrives; take the first train that comes; etc.), 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 (according to general principles for uses of English verb forms): If he is sleeping when we arrive, we shan't wake him. (present progressive) Will you wake him if he hasn't stirred by 10 o'clock? (present perfect) If you have been working for more than ten hours when he returns, he will take your place. (present perfect progressive)
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: If you should make a mistake, ... (equivalent to "If you make a mistake") Should you make a mistake, ... (inverted form equivalent to the above). If you should be young, ... (equivalent to "If you are young") Should you be young, ... (inverted form equivalent to the above)
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 (often involving polite expressions) 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" (meaning "if you go eastwards a mile, you will see it").
Although the consequence in first conditional sentences is usually expressed using the will (or shall) future (usually the simple future, though future progressive, future perfect and future perfect progressive are used as appropriate), 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 (consequent on a possible future event): If it rains this afternoon, come round to my place! (imperative) If it rains this afternoon, we can/could/should/may/might find somewhere to shelter. (other modals) If it rains this afternoon, then yesterday's weather forecast was wrong. (deduction about the past) If it rains this afternoon, your garden party is doomed. (deduction placed in the present)
A particular case involves a condition clause that expresses a goal (this is often done using the be + to construction, the going-to future or the verb want), 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". If we want to succeed, we have to try harder. If you are to get your pocket money, you must start behaving yourself.
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 (for past time frames the third conditional is used). In the normal form of the second conditional, the condition clause is in the past tense (although it does not have past meaning—see Use of the past subjunctive), and the consequence is expressed using the conditional construction with the auxiliary would: If I liked parties, I would attend more of them. If it rained tomorrow, people would dance in the street.
The past tense (simple past or past progressive) 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 (were otherwise preferred), although the phrase if I were you is common in colloquial language. For more details see . If I (he, she, it) were rich, there would be plenty of money available for this project. If I (he, she, it) were speaking, you would not be allowed to interrupt like that.
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 (particularly if it has hypothetical future reference); if this is done, then inversion can be applied here too: If I were rich, ... / If I were to be rich, ... / Were I (to be) rich, ... If I flew, ... / If I were to fly, ... / Were I to fly, ...
Another possible pattern is if it weren't for... (inverted form: were it not 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.