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The principle of sufficient reason states that everything must have a reason or a cause. The modern〔From Hamilton 1860:67" In modern times, the attention of philosophers was called to this law of Leibnitz, who, on the two principles of Reason and of Contradiction, founded the whole edifice of his philosophy.3 3 See Théodicée, § 44. Monadologie, §§ 81, 82. —ED."〕 formulation of the principle is usually attributed to Gottfried Leibniz,〔There are numerous anticipations. One often pointed to is in Anselm of Canterbury: his phrase ''quia Deus nihil sine ratione facit''() and the formulation of the ontological argument for the existence of God. A clearer connection is with the cosmological argument for the existence of God. The principle can be seen in both Thomas Aquinas and William of Ockham. Leibniz formulated it, but was not an originator. See chapter on Leibniz and Spinoza in A. O. Lovejoy, ''The Great Chain of Being''.〕 although the idea was conceived and utilized in various philosophers who preceded him, including Anaximander, Parmenides, Archimedes, Plato and Aristotle,〔Hamilton 1860:66〕 Cicero,〔Hamilton 1860:66〕 Avicenna, Thomas Aquinas, Anaximander of Miletus, and Spinoza.〔.〕 Some philosophers have associated the principle of sufficient reason with "''ex nihilo nihil fit''".,〔Alexander R. Pruss (2007) "''Ex Nihilo Nihil Fit: Augments new and old for the Principle of Sufficient Reason''" in ''Explication Topic in Contemporary Philosophy'' Ch. 14〕〔Hamilton attributes this expression to Cicero; Hamilton 1860:66〕 Hamilton identified the laws of inference modus ponens with the "law of Sufficient Reason, or of Reason and Consequent" and modus tollens with its contrapositive expression.〔From Hamilton 1860:241–242: “2°, "If the essential nature of an Hypothetical Syllogism consist in this, – that the subsumption affirms or denies one or other of the two parts of a thought, standing to each other in the relation of the thing conditioning and the thing conditioned, it will be the law of an hypothetical syllogism, that, – If the condition or antecedent be affirmed, so also must be the conditioned or consequent, and that if the conditioned or consequent be denied, so likewise must be the condition or antecedent. But this is manifestly nothing else than the law of Sufficient Reason, or of Reason and Consequent." 1 The principle of this syllogism is thus variously enounced: ''Posita conditione, ponitur conditionatum, sublato conditionato, tlitur conditio''. Or otherwise, ''a ratione ad rationatum, a negatione rationati ad negationem rationis, valet consequentia''. The one alternative of either rule being regulative of ''modus ponens'', the other of the ''modus tollens''. 2 1 Esser, Logik, I 91, p. 174. —ED. 2 See Kant, Logik §§ 75–76 . Krug, Logik, § 82. —ED." See in particular Hamilton's discussion that leads to this quote starting at page 239ff.〕 ==Formulation== The principle has a variety of expressions, all of which are perhaps best summarized by the following: *For every entity ''X'', if ''X'' exists, then there is a sufficient explanation for why ''X'' exists. *For every event ''E'', if ''E'' occurs, then there is a sufficient explanation for why ''E'' occurs. *For every proposition ''P'', if ''P'' is true, then there is a sufficient explanation for why ''P'' is true. A sufficient explanation may be understood either in terms of ''reasons'' or ''causes,'' for like many philosophers of the period, Leibniz did not carefully distinguish between the two. The resulting principle is very different, however, depending on which interpretation is given. It is an open question whether the principle of sufficient reason can be applied to axioms within a logic construction like a mathematical or a physical theory, because axioms are propositions accepted as having no justification possible within the system . The principle declares that all propositions considered to be true within a system should be deducible from the set axioms at the base of the construction (with some theoretical exceptions: see Gödel's theorem). 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「principle of sufficient reason」の詳細全文を読む スポンサード リンク
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