15 ideas
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. |
15927 | Definition just needs negation, known variables, conjunction, disjunction, substitution and quantification [Weyl, by Lavine] |
Full Idea: For mathematics, Weyl arrived (by 1917) at a satisfactory list of definition principles: negation, identification of variables, conjunction, disjunction, substitution of constants, and existential quantification over the domain. | |
From: report of Hermann Weyl (works [1917]) by Shaughan Lavine - Understanding the Infinite V.3 | |
A reaction: Lavine summarises this as 'first-order logic with parameters'. |
8828 | Truth is rational acceptability [Putnam] |
Full Idea: Truth, in the only sense in which we have a vital and working notion of it, is rational acceptability. | |
From: Hilary Putnam (Why Reason Can't be Naturalized [1981]) | |
A reaction: I smell a circularity somewhere in there, probably in 'rational', though it could be in 'acceptable'. Putnams's views on truth tend to shift a lot. He denies that evolutionary survival is a criterion. |
190 | If asked whether justice itself is just or unjust, you would have to say that it is just [Plato] |
Full Idea: If someone asked me 'Is justice itself just or unjust?' I should answer that it was just, wouldn't you? I agree. | |
From: Plato (Protagoras [c.380 BCE], 330c) |
20184 | The only real evil is loss of knowledge [Plato] |
Full Idea: The only real kind of faring ill is the loss of knowledge. | |
From: Plato (Protagoras [c.380 BCE], 345b) | |
A reaction: This must crucially involve the intellectualist view (of Socrates) that virtuos behaviour results from knowledge, and moral wickedness is the result of ignorance. It is hard to see how forgetting a phone number is evil. |
20185 | The most important things in life are wisdom and knowledge [Plato] |
Full Idea: It would be shameful indeed to say that wisdom and knowledge are anything but the most powerful forces in human activity. | |
From: Plato (Protagoras [c.380 BCE], 352d) | |
A reaction: He lumps wisdom and knowledge together, and I think we can take 'knowledge' to mean something like understanding, because obviously mere atomistic propositional knowledge can be utterly trivial. |
191 | Everything resembles everything else up to a point [Plato] |
Full Idea: Everything resembles everything else up to a point. | |
From: Plato (Protagoras [c.380 BCE], 331d) |
203 | Courage is knowing what should or shouldn't be feared [Plato] |
Full Idea: Knowledge of what is and is not to be feared is courage. | |
From: Plato (Protagoras [c.380 BCE], 360d) |
202 | No one willingly and knowingly embraces evil [Plato] |
Full Idea: No one willingly goes to meet evil, or what he thinks is evil. | |
From: Plato (Protagoras [c.380 BCE], 358d) | |
A reaction: Presumably people who actively choose satanism can override this deep-seated attitude. But their adherence to evil usually seems to be rather restrained. A danger of tautology with ideas like this. |
193 | Some things are good even though they are not beneficial to men [Plato] |
Full Idea: 'Do you mean by good those things that are beneficial to men?' 'Not only those. I call some things which are not beneficial good as well'. | |
From: Plato (Protagoras [c.380 BCE], 333e) | |
A reaction: Examples needed, but this would be bad news for utilitarians. Good health is not seen as beneficial if it is taken for granted. Not being deaf. |
197 | Some pleasures are not good, and some pains are not evil [Plato] |
Full Idea: There are some pleasures which are not good, and some pains which are not evil. | |
From: Plato (Protagoras [c.380 BCE], 351d) | |
A reaction: Sadism and child birth. Though Bentham (I think) says that there is nothing good about the pain, since the event would obviously be better without it. |
200 | People tend only to disapprove of pleasure if it leads to pain, or prevents future pleasure [Plato] |
Full Idea: The only reason the common man disapproves of pleasures is if they lead to pain and deprive us of future pleasures. | |
From: Plato (Protagoras [c.380 BCE], 354a) | |
A reaction: Plato has a strong sense that some pleasures are just innately depraved and wicked. If those pleasure don't hurt anyone, it is very hard to pinpoint what is wrong with them. |
189 | If we punish wrong-doers, it shows that we believe virtue can be taught [Plato] |
Full Idea: Athenians inflict punishment on wrong-doers, which shows that they too think it possible to impart and teach goodness. | |
From: Plato (Protagoras [c.380 BCE], 324c) |
188 | Socrates did not believe that virtue could be taught [Plato] |
Full Idea: Socrates: I do not believe that virtue can be taught. | |
From: Plato (Protagoras [c.380 BCE], 320b) |
204 | Socrates is contradicting himself in claiming virtue can't be taught, but that it is knowledge [Plato] |
Full Idea: Socrates is contradicting himself by saying virtue is not teachable, and yet trying to demonstrate that every virtue is knowledge. | |
From: Plato (Protagoras [c.380 BCE], 361b) |