37 ideas
| 18073 | Dummett says classical logic rests on meaning as truth, while intuitionist logic rests on assertability [Dummett, by Kitcher] |
| Full Idea: Dummett argues that classical logic depends on the choice of the concept of truth as central to the theory of meaning, while for the intuitionist the concept of assertability occupies this position. | |
| From: report of Michael Dummett (The philosophical basis of intuitionist logic [1973]) by Philip Kitcher - The Nature of Mathematical Knowledge 06.5 | |
| A reaction: Since I can assert any nonsense I choose, this presumably means 'warranted' assertability, which is tied to the concept of proof in mathematics. You can reason about falsehoods, or about uninterpreted variables. Can you 'assert' 'Fx'? |
| 17610 | The Axiom of Choice paradoxically allows decomposing a sphere into two identical spheres [Maddy] |
| Full Idea: One feature of the Axiom of Choice that troubled many mathematicians was the so-called Banach-Tarski paradox: using the Axiom, a sphere can be decomposed into finitely many parts and those parts reassembled into two spheres the same size as the original. | |
| From: Penelope Maddy (Defending the Axioms [2011], 1.3) | |
| A reaction: (The key is that the parts are non-measurable). To an outsider it is puzzling that the Axiom has been universally accepted, even though it produces such a result. Someone can explain that, I'm sure. |
| 15845 | It seems absurd that seeing a person's limbs, the one is many, and yet the many are one [Plato] |
| Full Idea: Someone first distinguishes a person's limbs and parts and asks your agreement that all the parts are identical with that unity, then ridicules you that you have to admit one is many, and indefinitely many, and again that the many are only only one thing. | |
| From: Plato (Philebus [c.353 BCE], 14e) | |
| A reaction: This is a passing aporia, but actually seems to approach the central mystery of the metaphysics of identity. A thing can't be a 'unity' if there are not things to unify? So what sorts of 'unification' are there? |
| 17620 | Critics of if-thenism say that not all starting points, even consistent ones, are worth studying [Maddy] |
| Full Idea: If-thenism denies that mathematics is in the business of discovering truths about abstracta. ...[their opponents] obviously don't regard any starting point, even a consistent one, as equally worthy of investigation. | |
| From: Penelope Maddy (Defending the Axioms [2011], 3.3) | |
| A reaction: I have some sympathy with if-thenism, in that you can obviously study the implications of any 'if' you like, but deep down I agree with the critics. |
| 19057 | Classical quantification is an infinite conjunction or disjunction - but you may not know all the instances [Dummett] |
| Full Idea: Classical quantification represents an infinite conjunction or disjunction, and the truth-value is determined by the infinite sum or product of the instances ....but this presupposes that all the instances already possess determinate truth-values. | |
| From: Michael Dummett (The philosophical basis of intuitionist logic [1973], p.246) | |
| A reaction: In the case of the universal quantifier, Dummett is doing no more than citing the classic empiricism objection to induction - that you can't make the universal claim if you don't know all the instances. The claim is still meaningful, though. |
| 17605 | Hilbert's geometry and Dedekind's real numbers were role models for axiomatization [Maddy] |
| Full Idea: At the end of the nineteenth century there was a renewed emphasis on rigor, the central tool of which was axiomatization, along the lines of Hilbert's axioms for geometry and Dedekind's axioms for real numbers. | |
| From: Penelope Maddy (Defending the Axioms [2011], 1.3) |
| 17625 | If two mathematical themes coincide, that suggest a single deep truth [Maddy] |
| Full Idea: The fact that two apparently fruitful mathematical themes turn out to coincide makes it all the more likely that they're tracking a genuine strain of mathematical depth. | |
| From: Penelope Maddy (Defending the Axioms [2011], 5.3ii) |
| 9867 | It is absurd to define a circle, but not be able to recognise a real one [Plato] |
| Full Idea: It will be ridiculous if our student knows the definition of the circle and of the divine sphere itself, but cannot recognize the human sphere and these our circles, used in housebuilding. | |
| From: Plato (Philebus [c.353 BCE], 62a) | |
| A reaction: This is the equivalent of being able to recite numbers, but not to count objects. It also resembles Molyneux's question (to Locke), of whether recognition by one sense entails recognition by others. Nice (and a bit anti-platonist!). |
| 9865 | Daily arithmetic counts unequal things, but pure arithmetic equalises them [Plato] |
| Full Idea: The arithmetic of the many computes sums of unequal units, such as two armies, or two herds, ..but philosopher's arithmetic computes when it is guaranteed that none of those infinitely many units differed in the least from any of the others. | |
| From: Plato (Philebus [c.353 BCE], 56d) | |
| A reaction: But of course 'the many' are ironing out the differences too, when they say there are 'three armies'. Shocking snob, Plato. Even philosophers are interested in the difference between three armies and three platoons. |
| 17615 | Every infinite set of reals is either countable or of the same size as the full set of reals [Maddy] |
| Full Idea: One form of the Continuum Hypothesis is the claim that every infinite set of reals is either countable or of the same size as the full set of reals. | |
| From: Penelope Maddy (Defending the Axioms [2011], 2.4 n40) |
| 17618 | Set-theory tracks the contours of mathematical depth and fruitfulness [Maddy] |
| Full Idea: Our set-theoretic methods track the underlying contours of mathematical depth. ...What sets are, most fundamentally, is markers for these contours ...they are maximally effective trackers of certain trains of mathematical fruitfulness. | |
| From: Penelope Maddy (Defending the Axioms [2011], 3.4) | |
| A reaction: This seems to make it more like a map of mathematics than the actual essence of mathematics. |
| 17614 | The connection of arithmetic to perception has been idealised away in modern infinitary mathematics [Maddy] |
| Full Idea: Ordinary perceptual cognition is most likely involved in our grasp of elementary arithmetic, but ...this connection to the physical world has long since been idealized away in the infinitary structures of contemporary pure mathematics. | |
| From: Penelope Maddy (Defending the Axioms [2011], 2.3) | |
| A reaction: Despite this, Maddy's quest is for a 'naturalistic' account of mathematics. She ends up defending 'objectivity' (and invoking Tyler Burge), rather than even modest realism. You can't 'idealise away' the counting of objects. I blame Cantor. |
| 14503 | If a mixture does not contain measure and proportion, it is corrupted and destroyed [Plato] |
| Full Idea: Any kind of mixture that does not ...possess measure or the nature of proportion will necessarily corrupt its ingredients and most of all itself. For there would be no blending in such cases but really an unconnected medley, and ruin what contains it. | |
| From: Plato (Philebus [c.353 BCE], 64d) | |
| A reaction: My guess is that Plato is thinking of the decay of living things when they die, losing the proportions of psuché, and then applying this to the unity of inanimate objects as well. One might compare Leibniz's monads. |
| 15857 | Any mixture which lacks measure and proportion doesn't even count as a mixture at all [Plato] |
| Full Idea: Any blend [mixture] which does not have measure or the nature of proportion in any way whatsoever, of necessity destroys both its ingredients and, primarily, itself. It is truly no blend at all, but a kind of unblended disaster. | |
| From: Plato (Philebus [c.353 BCE], 64e) | |
| A reaction: Obviously there can be chaotic mixtures, but I guess Plato is picking out mixtures about which we can say something |
| 4447 | If the good is one, is it unchanged when it is in particulars, and is it then separated from itself? [Plato] |
| Full Idea: If man is one, and the good is one, how are they supposed to exist? Do they stay the same even though they are found in many things at the same time, and are they then entirely separated from themselves, which seems most impossible of all? | |
| From: Plato (Philebus [c.353 BCE], 15a) | |
| A reaction: Presumably Plato anguishes over this because he thinks Forms are self-predicating (the Good is good). Big mistake. The Good fathers good particulars which resemble itself, but are diluted? |
| 15856 | A thing can become one or many, depending on how we talk about it [Plato] |
| Full Idea: It is through discourse that the same thing flits around, becoming one and many in all sorts of ways. | |
| From: Plato (Philebus [c.353 BCE], 15d) | |
| A reaction: This is not scepticism about wholes on Plato's part, but a reminder of an obvious fact, that in thought we can break the world up and put it back together again. It is a touchstone of the debate, though. |
| 374 | If one object is divided into its parts, someone can then say that one are many and many is one [Plato] |
| Full Idea: Someone can theoretically divide an object into constituent parts, concede that they are one object, and then claim that therefore the one is many and the many are one. | |
| From: Plato (Philebus [c.353 BCE], 14e) |
| 389 | How can you be certain about aspects of the world if they aren't constant? [Plato] |
| Full Idea: Could we attribute certainty to studying aspects of the world, such as how it arose, or acts, or is acted upon, when none of them ever was or will be constant? Of course not. | |
| From: Plato (Philebus [c.353 BCE], 59b) |
| 19055 | Stating a sentence's truth-conditions is just paraphrasing the sentence [Dummett] |
| Full Idea: An ability to state the condition for the truth of a sentence is, in effect, no more than an ability to express the content of the sentence in other words. | |
| From: Michael Dummett (The philosophical basis of intuitionist logic [1973], p.224) | |
| A reaction: Alternatively, if you give something other than a paraphrase of the sentence as its meaning (such as a proof of its truth), then you seem to have departed from your target sentence. Can we reduce and eliminate our sentences in this way? |
| 19056 | If a sentence is effectively undecidable, we can never know its truth conditions [Dummett] |
| Full Idea: If a sentence is effectively undecidable, the condition which must obtain for it to be true is not one which we are capable of recognising whenever it obtains, or of getting ourselves in a position to do so. | |
| From: Michael Dummett (The philosophical basis of intuitionist logic [1973], p.225) | |
| A reaction: The instances of 'undecidable' sentences are most clearly seen in mathematics, such as the Continuum Hypothesis or Goldbach's Conjecture, or anything involving vast infinite cardinals. But do you need precise truth-conditions for meaning? |
| 19054 | Meaning as use puts use beyond criticism, and needs a holistic view of language [Dummett] |
| Full Idea: If use constitutes meaning, it might seem that use is beyond criticism. ....But such an attitude can, ultimately, be supported onlly by the adoption of a holistic view of language. | |
| From: Michael Dummett (The philosophical basis of intuitionist logic [1973], p.218) | |
| A reaction: Dummett goes on to say that the rejection of the holistic view of mathematical meaning leads to his preference for intuitionistic logic. |
| 390 | If goodness involves moderation and proportion, then it seems to be found in beauty [Plato] |
| Full Idea: Moderation and proportion seem, in effect, to be beauty and excellence. So now this property we're looking for, goodness, has taken refuge in beauty. | |
| From: Plato (Philebus [c.353 BCE], 64e) |
| 392 | Neither intellect nor pleasure are the good, because they are not perfect and self-sufficient [Plato] |
| Full Idea: Both intellect and pleasure are completely absolved of being the good itself, since they both lack independence, that is, sufficiency and perfection. | |
| From: Plato (Philebus [c.353 BCE], 67a) | |
| A reaction: This seems to be Plato disagreeing with Socrates, who sees reason and intellect as central to morality. Presumable he means that the good should be a primitive. Why is pleasure not sufficient? |
| 391 | The good involves beauty, proportion and truth [Plato] |
| Full Idea: If we are unable to net the good in a single concept, three must capture it: namely, beauty, proportion and truth. | |
| From: Plato (Philebus [c.353 BCE], 65a) | |
| A reaction: Very interesting. More illuminating than the discussion of the Good in 'Republic'. Is a handsome and honest murderer good? Is beauty part of the nature of the good, or a hallmark of it? |
| 393 | Good first, then beauty, then reason, then knowledge, then pleasure [Plato, by PG] |
| Full Idea: Good is supreme, followed by beauty, then reason, then knowledge, then pure pleasure, then mixed pleasure. | |
| From: report of Plato (Philebus [c.353 BCE], 67a) by PG - Db (ideas) | |
| A reaction: He tells us that pure pleasures are simple pleasures. Epicurus presumably read this. No mention of truth, unless that is part of reason. Why does he value beauty so highly? |
| 385 | Some of the pleasures and pains we feel are false [Plato] |
| Full Idea: Living beings experience pleasures and pains which seem, and indeed are, false. | |
| From: Plato (Philebus [c.353 BCE], 42c) | |
| A reaction: The idea that there are 'authentic' pleasures and pains needs some investigation. Misguided anger is a false pain? Vanity is a false pleasure? |
| 387 | A small pure pleasure is much finer than a large one contaminated with pain [Plato] |
| Full Idea: A tiny little pleasure is, if uncontaminated by pain, always more pleasant, truer and finer than a large amount. | |
| From: Plato (Philebus [c.353 BCE], 53b) | |
| A reaction: More Platonic puritanism. Is a complete absence of pleasure the highest pleasure of all? I don't think I understand 'truer'. Why would a pleasure be false because it is intense? |
| 379 | The good must be sufficient and perfect, and neither intellect nor pleasure are that [Plato] |
| Full Idea: Neither pleasure nor intellect comprises the good. If it did it would have to be sufficient and perfect. | |
| From: Plato (Philebus [c.353 BCE], 22b) | |
| A reaction: Seems sensible. I can't make sense of any vision of the good which consists of suppressing some aspect of human nature. (Hm. Our capacity for violence?) |
| 376 | Would you prefer a life of pleasure without reason, or one of reason without pleasure? [Plato] |
| Full Idea: Try thinking about the life of pleasure without reason, and the life of reason without pleasure. | |
| From: Plato (Philebus [c.353 BCE], 20e) | |
| A reaction: I suspect that we see the two as more deeply entangled that Plato did. It would be hard to motivate reasoning if we didn't enjoy it. Pleasure without reason sound dire. |
| 371 | Reason, memory, truth and wisdom are far better than pleasure, for those who can attain them [Plato] |
| Full Idea: My contention is that reason, intellect, memory - along with correct belief and true calculation - are far better than pleasure for all creatures capable of attaining them. | |
| From: Plato (Philebus [c.353 BCE], 11b) | |
| A reaction: Why? Is it better to understand deeply, or to act well? Can we just say there is objective good and subjective good, and they have little in common? Depressed heroes. |
| 373 | Pleasure is certainly very pleasant, but it doesn't follow that all pleasures are good [Plato] |
| Full Idea: The pleasantness of pleasure is not in dispute, but where we say the majority of pleasures are bad, though some are good, you are attributing goodness to all of them. | |
| From: Plato (Philebus [c.353 BCE], 13b) | |
| A reaction: Bentham's plausible view is that the feeling of pleasure is always good, and the badness is in some other aspect of the event. Compare sadistic fantasy with sadistic action. |
| 382 | It is unlikely that the gods feel either pleasure or pain [Plato] |
| Full Idea: It is unlikely that the gods feel pleasure or the opposite. | |
| From: Plato (Philebus [c.353 BCE], 33b) | |
| A reaction: Compare Idea 383. |
| 381 | We feel pleasure when we approach our natural state of harmony [Plato] |
| Full Idea: When harmony is being restored, and the natural state of harmony is approached, then pleasure arises. | |
| From: Plato (Philebus [c.353 BCE], 31d) | |
| A reaction: The supreme value of harmony was important to Plato, but most of us are less convinced, I suspect. The way to achieve harmony is to avoid anything stressful. |
| 386 | Intense pleasure and pain are not felt in a good body, but in a worthless one [Plato] |
| Full Idea: Intensity of pleasure and pain is to be found not in a good state of body and soul, but in a worthless one. | |
| From: Plato (Philebus [c.353 BCE], 45e) | |
| A reaction: This just seems to be Plato's puritanism. How can you criticise someone for experience genuine intense pain? Experiencing intense pleasure is no crime, but pursuit of it might be. |
| 388 | Hedonists must say that someone in pain is bad, even if they are virtuous [Plato] |
| Full Idea: A hedonist must say that someone who happens to be feeling pain rather than pleasure is, as long as the pain lasts, a bad man, even if he is the most virtuous man in the world. | |
| From: Plato (Philebus [c.353 BCE], 55b) |
| 377 | If you lived a life of maximum pleasure, would you still be lacking anything? [Plato] |
| Full Idea: Would you, Protarchus, gladly live your whole life experiencing only the greatest pleasure? Would you think you were still lacking anything? | |
| From: Plato (Philebus [c.353 BCE], 21a) | |
| A reaction: the pleasure machine problem |
| 378 | A life of pure pleasure with no intellect is the life of a jellyfish [Plato] |
| Full Idea: A life of pure pleasure with no intellect is not the life of a human being, but the life of a jellyfish. | |
| From: Plato (Philebus [c.353 BCE], 21c) |