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In classical logic, a contradiction consists of a logical incompatibility between two or more propositions. It occurs when the propositions, taken together, yield two conclusions which form the logical, usually opposite inversions of each other. Illustrating a general tendency in applied logic, Aristotle's law of noncontradiction states that "One cannot say of something that it is and that it is not in the same respect and at the same time." By extension, outside of classical logic, one can speak of contradictions between actions when one presumes that their motives contradict each other. ==History== By creation of a paradox, Plato's ''Euthydemus'' dialogue demonstrates the need for the notion of ''contradiction''. In the ensuing dialogue Dionysodorus denies the existence of "contradiction", all the while that Socrates is contradicting him: :". . . I in my astonishment said: What do you mean Dionysodorus? I have often heard, and have been amazed to hear, this thesis of yours, which is maintained and employed by the disciples of Protagoras and others before them, and which to me appears to be quite wonderful, and suicidal as well as destructive, and I think that I am most likely to hear the truth about it from you. The dictum is that there is no such thing as a falsehood; a man must either say what is true or say nothing. Is not that your position?" Indeed, Dionysodorus agrees that "there is no such thing as false opinion . . . there is no such thing as ignorance" and demands of Socrates to "Refute me." Socrates responds "But how can I refute you, if, as you say, to tell a falsehood is impossible?".〔Dialog ''Euthydemus'' from ''The Dialogs of Plato translated by Benjamin Jowett'' appearing in: BK 7 ''Plato'': Robert Maynard Hutchins, editor in chief, 1952, ''Great Books of the Western World'', Encyclopædia Britannica, Inc., Chicago.〕 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「contradiction」の詳細全文を読む スポンサード リンク
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