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In logic, the converse of a categorical or implicational statement is the result of reversing its two parts. For the implication ''P'' → ''Q'', the converse is ''Q'' → ''P''. For the categorical proposition ''All S is P'', the converse is ''All P is S''. In neither case does the converse necessarily follow from the original statement.〔Robert Audi, ed. (1999), ''The Cambridge Dictionary of Philosophy'', 2nd ed., Cambridge University Press: "converse".〕 The categorical converse of a statement is contrasted with the contrapositive and the obverse. ==Implicational converse== Let ''S'' be a statement of the form ''P implies Q'' (''P'' → ''Q''). Then the converse of ''S'' is the statement ''Q implies P'' (''Q'' → ''P''). In general, the verity of ''S'' says nothing about the verity of its converse, unless the antecedent ''P'' and the consequent ''Q'' are logically equivalent. For example, consider the true statement "If I am a human, then I am mortal." The converse of that statement is "If I am mortal, then I am a human," which is not necessarily true. On the other hand, the converse of a statement with mutually inclusive terms remains true, given the truth of the original proposition. Thus, the statement "If I am a bachelor, then I am an unmarried man" is logically equivalent to "If I am an unmarried man, then I am a bachelor." A truth table makes it clear that ''S'' and the converse of ''S'' are not logically equivalent unless both terms imply each other: Going from a statement to its converse is the fallacy of affirming the consequent. ''However, if the statement ''S'' and its converse are equivalent (i.e. if ''P'' is true if and only if ''Q'' is also true), then affirming the consequent will be valid. 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「Converse (logic)」の詳細全文を読む スポンサード リンク
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