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Conditional sentences are sentences expressing factual implications, or hypothetical situations and their consequences. They are so called because the validity of the main clause of the sentence is ''conditional'' on the existence of certain circumstances, which may be expressed in a dependent clause or may be understood from the context. A full conditional sentence (one which expresses the condition as well as its consequences) therefore contains two clauses: the dependent clause expressing the condition, called the ''protasis''; and the main clause expressing the consequence, called the ''apodosis''.〔Haspelmath, Martin; König, Ekkehard; Oesterreicher, Wulf; Raible, Wolfgang: ''Language Typology and Language Universals'', Walter de Gruyter, 2001, p. 1002.〕 An example of such a sentence (in English) is the following: Here the condition is expressed by the clause "If it rains", this being the protasis, while the consequence is expressed by "the picnic will be cancelled", this being the apodosis. (The protasis may either precede or follow the apodosis; it is equally possible to say "The picnic will be cancelled if it rains".) In terms of logic, the protasis corresponds to the antecedent, and the apodosis to the consequent. Languages use a variety of grammatical forms and constructions in conditional sentences. The forms of verbs used in the protasis and apodosis are often subject to particular rules as regards their tense and mood. Many languages have a specialized type of verb form called the conditional mood – broadly equivalent in meaning to the English "would (do something)" – for use in some types of conditional sentence. ==Types of conditional sentence== There are various ways of classifying conditional sentences. One distinction is between those that state an implication between facts, and those that set up and refer to a hypothetical situation. There is also the distinction between conditionals that are considered factual or predictive, and those that are considered counterfactual or speculative (referring to a situation that did not or does not really exist). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Conditional sentence」の詳細全文を読む スポンサード リンク
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