| 12268 | Contradiction is impossible [Antisthenes (I), by Aristotle] |
| Full Idea: Antisthenes said that contradiction is impossible. | |
| From: report of Antisthenes (Ath) (fragments/reports [c.405 BCE]) by Aristotle - Topics 104b21 | |
| A reaction: Aristotle is giving an example of a 'thesis'. It should be taken seriously if a philosopher proposes it, but dismissed as rubbish if anyone else proposes it! No context is given for the remark. |
| 23917 | Contrary statements can both be reasonable, if they are meant in two different ways [Aristotle] |
| Full Idea: Contrary things can be reasonably held …because the contrary positions will stand if what is said is true in one way, but not true in another. | |
| From: Aristotle (Eudemian Ethics [c.333 BCE], 1235b17) | |
| A reaction: My strategy here is to clarify the unambiguous underlying propositions which are being expressed. There will then be either agreement, or flat contradiction. |
| 6561 | A thing cannot be both in and not-in the same thing (at a given time) [Aristotle] |
| Full Idea: It is impossible for the same thing at the same time both to be-in and not to be-in the same thing in the same respect. | |
| From: Aristotle (Metaphysics [c.324 BCE], 1005b19) | |
| A reaction: Aristotle is really discussing non-contradiction here, but this formulation is very close to Leibniz's Law (that two identical things must have identical properties). |
| 11281 | We cannot say that one thing both is and is not a man [Aristotle] |
| Full Idea: It is not possible to say truly at the same time that the same thing both is and is not a man. | |
| From: Aristotle (Metaphysics [c.324 BCE], 1006b33) |
| 1602 | For Aristotle predication is regulated by Non-Contradiction, because underlying stability is essential [Roochnik on Aristotle] |
| Full Idea: The Principle of Noncontradiction is for Aristotle the ultimate regulator of predication. In order for any predication to be significant it must refer to something definite and stable. | |
| From: comment on Aristotle (Metaphysics [c.324 BCE], 1011b13) by David Roochnik - The Tragedy of Reason p.152 |
| 1601 | The most certain basic principle is that contradictories can't be true at the same time [Aristotle] |
| Full Idea: The most certain of all basic principles is that contradictory propositions are not true at the same time. | |
| From: Aristotle (Metaphysics [c.324 BCE], 1011b13) | |
| A reaction: Principle of Noncontradiction |
| 11282 | Aristotle does not take the principle of non-contradiction for granted [Aristotle, by Politis] |
| Full Idea: Aristotle goes to great lengths to defend the principle of non-contradiction, and does not at all think that it is obviously true. | |
| From: report of Aristotle (Metaphysics [c.324 BCE], logic) by Vassilis Politis - Aristotle and the Metaphysics 5.1 |
| 9108 | From an impossibility anything follows [William of Ockham] |
| Full Idea: From an impossibility anything follows ('quod ex impossibili sequitur quodlibet'). | |
| From: William of Ockham (Summa totius logicae [1323], III.c.xxxvi) | |
| A reaction: The hallmark of a true logician, I suspect, is that this opinion is really meaningful and important to them. They yearn to follow the logic wherever it leads. Common sense would seem to say that absolutely nothing follows from an impossibility. |
| 15616 | If truth is just non-contradiction, we must take care that our basic concepts aren't contradictory [Hegel] |
| Full Idea: If truth were nothing more than lack of contradiction, one would have to examine first of all, with regard to each concept, whether it does not on its own account, contain an inner contradiction. | |
| From: Georg W.F.Hegel (Logic (Encyclopedia I) [1817], §33 Rem) | |
| A reaction: This is a very nice thought, which modern analytic philosophers, steeped in logic, should think about. It is always presumed that a contradiction is between a proposition and its negation, not some inner feature. |
| 21983 | Being and nothing are the same and not the same, which is the identity of identity and non-identity [Hegel] |
| Full Idea: Pure being and pure nothing are the same, ...but on the contrary they are not the same ...they are absolutely distinct. ...This is the identity of identity and non-identity. | |
| From: Georg W.F.Hegel (Science of Logic [1816], I.i.i.1C p.82,74), quoted by A.W. Moore - The Evolution of Modern Metaphysics 07.7 | |
| A reaction: Even Moore, who is very patient with Hegel, gets cross at this point, describing such talk as 'shocking'. He's not wrong. Moore later says that the reason in reality tolerates contradictions, but human understanding can't. |
| 21985 | The so-called world is filled with contradiction [Hegel] |
| Full Idea: The so-called world is never and nowhere without contradiction. (...but it is unable to endure it) | |
| From: Georg W.F.Hegel (Science of Logic [1816], I.i.ii.2C(b)), quoted by A.W. Moore - The Evolution of Modern Metaphysics 07.7 | |
| A reaction: [Second bit in Ency I §11] To clarify this one would need to understand 'so-called'. Note that his claim is not that the world contains occasional contradictions, but that the whole of reality is contradictory. I think this idea is nonsense. |
| 14787 | Self-contradiction doesn't reveal impossibility; it is inductive impossibility which reveals self-contradiction [Peirce] |
| Full Idea: It is an anacoluthon to say that a proposition is impossible because it is self-contradictory. It rather is thought so to appear self-contradictory because the ideal induction has shown it to be impossible. | |
| From: Charles Sanders Peirce (The Nature of Mathematics [1898], III) |
| 4531 | Our inability to both affirm and deny a single thing is merely an inability, not a 'necessity' [Nietzsche] |
| Full Idea: We are unable to affirm and to deny one and the same thing: this is a subjective empirical law, not the expression of any 'necessity', but only an inability. | |
| From: Friedrich Nietzsche (The Will to Power (notebooks) [1888], §516) | |
| A reaction: A remarkable claim, made by someone utterly gripped by relativism. I don't believe it. Why can't we do it? We experience it as a truth, not as a prejudice or mental block. I say it reflects reality - there is only one set of facts. |
| 22642 | Man has an intense natural interest in the consistency of his own thinking [James] |
| Full Idea: After man's interest in breathing freely, the greatest of all his interests (because it never fluctuates or remits….) is his interest in consistency, in feeling that what he now thinks goes with what he thinks on other occasions. | |
| From: William James (The Pragmatist Account of Truth [1908], 'Seventh') | |
| A reaction: People notoriously contradict themselves all the time, but I suspect that it is when they get out of their depth in complexities such as politics. They probably achieve great consistency within their own expertise, and in common knowledge. |
| 17632 | Non-contradiction was learned from instances, and then found to be indubitable [Russell] |
| Full Idea: The law of contradiction must have been originally discovered by generalising from instances, though, once discovered, it was found to be quite as indubitable as the instances. | |
| From: Bertrand Russell (Regressive Method for Premises in Mathematics [1907], p.274) |
| 6566 | The problem is to explain the role of contradiction in social life [Wittgenstein] |
| Full Idea: When a contradiction appears, we say: "I didn't mean it like that"; the civil status of a contradiction, or its status in civil life: there is the philosophical problem. | |
| From: Ludwig Wittgenstein (Philosophical Investigations [1952], §125), quoted by Robert Fogelin - Walking the Tightrope of Reason Ch.2 | |
| A reaction: The point is that logical concepts such as contradiction are conventional, and not all-or-nothing, so we might agree that you didn't really contradict yourself (when perhaps you uttered a witty ironic paradox). I don't see the problem as philosophical. |
| 9023 | If you say that a contradiction is true, you change the meaning of 'not', and so change the subject [Quine] |
| Full Idea: Those who regard the conjunction p.not-p as true think they are talking about negation, 'not', but this ceases to be recognisable as negation. The deviant logician's predicament is when he tries to deny the doctrine he only changes the subject. | |
| From: Willard Quine (Philosophy of Logic [1970], Ch.6) | |
| A reaction: The charge of 'changing the subject' has become a classic move in modern discussions of non-standard logics. It is an important idea in discussions of arguments, and is found in Kant's account of the Ontological Argument. |
| 6564 | To affirm 'p and not-p' is to have mislearned 'and' or 'not' [Quine] |
| Full Idea: To affirm a compound of the form 'p and not-p' is just to have mislearned one or both of these particles. | |
| From: Willard Quine (From Stimulus to Science [1995], p.23), quoted by Robert Fogelin - Walking the Tightrope of Reason Ch.1 | |
| A reaction: Quoted by Fogelin. This summarises the view of logic developed by the young Wittgenstein, that logical terms are 'operators', rather than referring terms. Of course the speaker may have a compartmentalised mind, or not understand 'p' properly. |
| 9123 | Someone standing in a doorway seems to be both in and not-in the room [Priest,G, by Sorensen] |
| Full Idea: Priest says there is room for contradictions. He gives the example of someone in a doorway; is he in or out of the room. Given that in and out are mutually exclusive and exhaustive, and neither is the default, he seems to be both in and not in. | |
| From: report of Graham Priest (What is so bad about Contradictions? [1998]) by Roy Sorensen - Vagueness and Contradiction 4.3 | |
| A reaction: Priest is a clever lad, but I don't think I can go with this. It just seems to be an equivocation on the word 'in' when applied to rooms. First tell me the criteria for being 'in' a room. What is the proposition expressed in 'he is in the room'? |
| 4633 | You cannot rationally deny the principle of non-contradiction, because all reasoning requires it [Baggini /Fosl] |
| Full Idea: Anyone who denies the principle of non-contradiction simultaneously affirms it; it cannot be rationally criticised, because it is presupposed by all rationality. | |
| From: J Baggini / PS Fosl (The Philosopher's Toolkit [2003], §1.12) | |
| A reaction: Nietzsche certainly wasn't afraid to ask why we should reject something because it is a contradiction. The 'logic of personal advantage' might allow logical contradictions. |
| 6565 | The law of noncontradiction makes the distinction between asserting something and denying it [Fogelin] |
| Full Idea: People who reject the law of noncontradiction obliterate any significant difference between asserting something and denying it; …this will not move anyone who genuinely opts either for silence or for madness. | |
| From: Robert Fogelin (Walking the Tightrope of Reason [2003], Ch.1) | |
| A reaction: This seems a sufficiently firm and clear assertion of the basic nature of this law. The only rival view seems to be that of Nietzsche (Idea 4531), but then you wonder how Nietzsche is in a position to assert the relativity of the law. |
| 19656 | Non-contradiction is unjustified, so it only reveals a fact about thinking, not about reality? [Meillassoux] |
| Full Idea: The principle of non-contradiction itself is without reason, and consequently it can only be the norm for what is thinkable by us, rather than for what is possible in the absolute sense. | |
| From: Quentin Meillassoux (After Finitude; the necessity of contingency [2006], 2) | |
| A reaction: This is not Meillassoux's view, but describes the modern heresy of 'correlationism', which ties all assessments of how reality is to our capacity to think about it. Personally I take logical non-contradiction to derive from non-contradiction in nature. |