| 192 | Only one thing can be contrary to something [Plato] |
| Full Idea: To everything that admits of a contrary there is one contrary and no more. | |
| From: Plato (Protagoras [c.380 BCE], 332c) | |
| A reaction: The sort of thing for which a modern philosopher would demand a proof (and then reject when the proof couldn't be found), where a Greek is happy to assert it as self-evident. I can't think of a counterexample. |
| 1697 | The contrary of good is bad, but the contrary of bad is either good or another evil [Aristotle] |
| Full Idea: What is contrary to a good thing is necessarily bad, as we see with health and sickness. But the contrary of bad is sometimes good, sometimes not, as we see with excess, opposed by both deficiency and moderation. | |
| From: Aristotle (Categories [c.331 BCE], 13b36) |
| 1698 | Both sides of contraries need not exist (as health without sickness, white without black) [Aristotle] |
| Full Idea: With contraries it is not necessary if one exists for the other to exist too, for if everyone were well health would exist but not sickness, and if everything were white whiteness would exist but not black. | |
| From: Aristotle (Categories [c.331 BCE], 14a06) |
| 24052 | From one thing alone we can infer its contrary [Aristotle] |
| Full Idea: One member of a pair of contraries is sufficient to discern both itself and its opposite. | |
| From: Aristotle (De Anima [c.329 BCE], 411a02) | |
| A reaction: This obviously requires prior knowledge of what the opposite is. He says you can infer the crooked from the straight. You can hardly use light in isolation to infer dark [see DA 418b17]. What's the opposite of a pig? |
| 4333 | Contraries are by definition as far distant as possible from one another [Aristotle] |
| Full Idea: Contraries are by definition as far distant as possible from one another. | |
| From: Aristotle (Nicomachean Ethics [c.334 BCE], 1108b33) | |
| A reaction: A nice concept and definition. Note that it is being used about ethics (the mean), not just about pure logic or mathematics. |
| 1708 | In "Callias is just/not just/unjust", which of these are contraries? [Aristotle] |
| Full Idea: Take, for example, "Callias is just", "Callias is not just", and "Callias is unjust"; which of these are contraries? | |
| From: Aristotle (On Interpretation [c.330 BCE], 23a31) |
| 608 | There is no middle ground in contradiction, but there is in contrariety [Aristotle] |
| Full Idea: With contradiction there can be no intermediate state, whereas with contrariety there can be. | |
| From: Aristotle (Metaphysics [c.324 BCE], 1055b02) |
| 1684 | Two falsehoods can be contrary to one another [Aristotle] |
| Full Idea: There are falsehoods which are contrary to one another and cannot be the case together e.g. that a man is a horse or a cow. | |
| From: Aristotle (Posterior Analytics [c.327 BCE], 88a29) |
| 16854 | Contrary pairs entail contradictions; one member entails negation of the other [Lipton] |
| Full Idea: All pairs of contraries entail a pair of contradictories, since one member of such a pair always entails the negation of the other. P&Q and not-P are contraries, but the first entails P, which is contradictory of not-P. | |
| From: Peter Lipton (Inference to the Best Explanation (2nd) [2004], 09 'Is the best') |