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Moore's paradox concerns the apparent absurdity involved in asserting a first-person present-tense sentence such as, "It's raining, but I don't believe that it is raining" or "It's raining but I believe that it is not raining." The first author to note this apparent absurdity was G. E. Moore. These 'Moorean' sentences, as they have become known, are paradoxical in that while they appear absurd, they nevertheless: # Can be true, # Are (logically) consistent, and moreover # Are not (obviously) contradictions. The term 'Moore's paradox' is attributed to Ludwig Wittgenstein, who considered the paradox Moore's most important contribution to philosophy. Wittgenstein wrote about the paradox extensively in his later writings, which brought Moore's paradox the attention it would not have otherwise received. Moore's paradox has also been connected to many other of the well-known logical paradoxes including, though not limited to, the liar paradox, the knower paradox, the unexpected hanging paradox, and the preface paradox. There is currently no generally accepted explanation of Moore's paradox in the philosophical literature. However, while Moore's paradox remains a philosophical curiosity, Moorean-type sentences are used by logicians, computer scientists, and those working in the artificial intelligence community as examples of cases in which a knowledge, belief, or information system is unsuccessful in updating its knowledge/belief/information store in light of new or novel information. ==The problem== Since Jaakko Hintikka's seminal treatment of the problem, it has become standard to present Moore's paradox by explaining why it is absurd to assert sentences that have the logical form: "P and NOT(I believe that P)" or "P and I believe that NOT-P." Philosophers nowadays refer to these, respectively, as the omissive and commissive versions of Moore's paradox. Moore himself presented the problem in two ways.〔 The first more fundamental way of setting the problem up starts from the following three premises: # It can be true at a particular time both that P, and that I do not believe that P. # I can assert or believe one of the two at a particular time. # It is absurd to assert or believe both of them at the same time. I can assert that it is raining at a particular time. I can assert that I don't believe that it is raining at a particular time. If I say both at the same time, I am saying or doing something absurd. But the content of what I say -- the proposition the sentence expresses -- is perfectly consistent: it may well be raining, and I may not believe it. So why cannot I assert that it is so? Moore presents the problem in a second, distinct, way: # It is not absurd to assert the past-tense counterpart, e.g. "It was raining, but I did not believe that it was raining." # It is not absurd to assert the second- or third-person counterparts to Moore's sentences, e.g. "It is raining, but ''you'' do not believe that it is raining," or "Michael is dead, but ''they'' do not believe that he is." # It is absurd to assert the present-tense "It is raining and I don't believe that it is raining." I can assert that I ''was'' a certain way, e.g. believing it was raining when it wasn't, and that you, he, or they, ''are'' that way but not that I ''am'' that way. Subsequent philosophers have further noted that there is also an apparent absurdity in asserting a first-person ''future-tense'' sentence such as "It will be raining, and I will believe that it is not raining." However, when it does not specify an exact time for when the belief is mistaken, the proposition will tend to be true at some point in the future - its negation would imply that "Every time I believe it's not raining, it will not be raining", which is unlikely since human beliefs are often mistaken. Many philosophers -- though by no means all -- also hold that Moore's paradox arises not only at the level of assertion but also at the level of belief. Interestingly, one who believes an instance of a Moorean sentence is tantamount to one who is subject to or engaging in self-deception, at least on one standard way of describing it. 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「Moore's paradox」の詳細全文を読む スポンサード リンク
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