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The Cartesian circle is a potential mistake in reasoning attributed to René Descartes. Descartes argues – for example, in the third of his ''Meditations on First Philosophy'' – that whatever one clearly and distinctly perceives is true: "I now seem to be able to lay it down as a general rule that whatever I perceive very clearly and distinctly is true." (AT VII 35)〔"AT" refers to ''Oeuvres de Descartes'', ed. by Charles Adam and Paul Tannery.〕 He goes on in the same Meditation to argue for the existence of a benevolent God, in order to defeat his skeptical argument in the first Meditation from the possibility that God be a deceiver. He then says that without his knowledge of God's existence, none of his knowledge could be certain. The argument takes this form: (1) Descartes' proof of the reliability of clear and distinct perceptions takes as a premise God's existence as a non-deceiver. (2) Descartes' proofs of God's existence presuppose the reliability of clear and distinct perceptions. ==Descartes' contemporaries== Many commentators, both at the time that Descartes wrote and since, have argued that this involves a circular argument, as he relies upon the principle of clarity and distinctness to argue for the existence of God, and then claims that God is the guarantor of his clear and distinct ideas. The first person to raise this criticism was Antoine Arnauld, in the "Second Set of Objections" to the ''Meditations'': "you are not yet certain of the existence of God, and you say that you are not certain of anything. It follows from this that you do not yet clearly and distinctly know that you are a thinking thing, since, on your own admission, that knowledge depends on the clear knowledge of an existing God; and this you have not proved in the passage where you draw the conclusion that you clearly know what you are." (AT VII 124–125) Descartes' own response to this criticism, in his "Author's Replies to the Second Set of Objections", is first to give what has become known as the Memory response; he points out that in the fifth Meditation (at AT VII 69–70) he did not say that he needed God to guarantee the truth of his clear and distinct ideas, only to guarantee his memory: "when I said that we can know nothing for certain until we are aware that God exists, I expressly declared that I was speaking only of knowledge of those conclusions which can be recalled when we are no longer attending to the arguments by means of which we deduced them." (AT VII 140) Secondly, he explicitly denies that the ''cogito'' is an inference: "When someone says 'I am thinking, therefore I am, or I exist' he does not deduce existence from thought by means of a syllogism, but recognizes it as something self-evident by a simple intuition of the mind." (AT VII 140) Finally, he points out that the certainty of clear and distinct ideas does not depend upon God's guarantee (AT VII 145–146). The ''cogito'' in particular is self-verifying, indubitable, immune to the strongest doubt. 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「Cartesian circle」の詳細全文を読む スポンサード リンク
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