39 ideas
| 13886 | Later Frege held that definitions must fix a function's value for every possible argument [Frege, by Wright,C] |
| Full Idea: Frege later became fastidious about definitions, and demanded that they must provide for every possible case, and that no function is properly determined unless its value is fixed for every conceivable object as argument. | |
| From: report of Gottlob Frege (Grundgesetze der Arithmetik 2 (Basic Laws) [1903]) by Crispin Wright - Frege's Concept of Numbers as Objects 3.xiv | |
| A reaction: Presumably definitions come in degrees of completeness, but it seems harsh to describe a desire for the perfect definition as 'fastidious', especially if we are talking about mathematics, rather than defining 'happiness'. |
| 9845 | We can't define a word by defining an expression containing it, as the remaining parts are a problem [Frege] |
| Full Idea: Given the reference (bedeutung) of an expression and a part of it, obviously the reference of the remaining part is not always determined. So we may not define a symbol or word by defining an expression in which it occurs, whose remaining parts are known | |
| From: Gottlob Frege (Grundgesetze der Arithmetik 2 (Basic Laws) [1903], §66) | |
| A reaction: Dummett cites this as Frege's rejection of contextual definitions, which he had employed in the Grundlagen. I take it not so much that they are wrong, as that Frege decided to set the bar a bit higher. |
| 10019 | Only what is logically complex can be defined; what is simple must be pointed to [Frege] |
| Full Idea: Only what is logically complex can be defined; what is simple can only be pointed to. | |
| From: Gottlob Frege (Grundgesetze der Arithmetik 2 (Basic Laws) [1903], §180), quoted by Harold Hodes - Logicism and Ontological Commits. of Arithmetic p.137 | |
| A reaction: Frege presumably has in mind his treasured abstract objects, such as cardinal numbers. It is hard to see how you could 'point to' anything in the phenomenal world that had atomic simplicity. Hodes calls this a 'desperate Kantian move'. |
| 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? |
| 9390 | Logic guides thinking, but it isn't a substitute for it [Rumfitt] |
| Full Idea: Logic is part of a normative theory of thinking, not a substitute for thinking. | |
| From: Ian Rumfitt (The Logic of Boundaryless Concepts [2007], p.13) | |
| A reaction: There is some sort of logicians' dream, going back to Leibniz, of a reasoning engine, which accepts propositions and outputs inferences. I agree with this idea. People who excel at logic are often, it seems to me, modest at philosophy. |
| 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!). |
| 9886 | Cardinals say how many, and reals give measurements compared to a unit quantity [Frege] |
| Full Idea: The cardinals and the reals are completely disjoint domains. The cardinal numbers answer the question 'How many objects of a given kind are there?', but the real numbers are for measurement, saying how large a quantity is compared to a unit quantity. | |
| From: Gottlob Frege (Grundgesetze der Arithmetik 2 (Basic Laws) [1903], §157), quoted by Michael Dummett - Frege philosophy of mathematics Ch.19 | |
| A reaction: We might say that cardinals are digital and reals are analogue. Frege is unusual in totally separating them. They map onto one another, after all. Cardinals look like special cases of reals. Reals are dreams about the gaps between cardinals. |
| 9889 | Real numbers are ratios of quantities [Frege, by Dummett] |
| Full Idea: Frege fixed on construing real numbers as ratios of quantities (in agreement with Newton). | |
| From: report of Gottlob Frege (Grundgesetze der Arithmetik 2 (Basic Laws) [1903]) by Michael Dummett - Frege philosophy of mathematics Ch.20 | |
| A reaction: If 3/4 is the same real number as 6/8, which is the correct ratio? Why doesn't the square root of 9/16 also express it? Why should irrationals be so utterly different from rationals? In what sense are they both 'numbers'? |
| 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. |
| 10553 | A number is a class of classes of the same cardinality [Frege, by Dummett] |
| Full Idea: For Frege, in 'Grundgesetze', a number is a class of classes of the same cardinality. | |
| From: report of Gottlob Frege (Grundgesetze der Arithmetik 2 (Basic Laws) [1903]) by Michael Dummett - Frege Philosophy of Language (2nd ed) Ch.14 |
| 10020 | Frege's biggest error is in not accounting for the senses of number terms [Hodes on Frege] |
| Full Idea: The inconsistency of Grundgesetze was only a minor flaw. Its fundamental flaw was its inability to account for the way in which the senses of number terms are determined. It leaves the reference-magnetic nature of the standard numberer a mystery. | |
| From: comment on Gottlob Frege (Grundgesetze der Arithmetik 2 (Basic Laws) [1903]) by Harold Hodes - Logicism and Ontological Commits. of Arithmetic p.139 | |
| A reaction: A point also made by Hofweber. As a logician, Frege was only concerned with the inferential role of number terms, and he felt he had captured their logical form, but it is when you come to look at numbers in natural language that he seem in trouble. |
| 9887 | Formalism misunderstands applications, metatheory, and infinity [Frege, by Dummett] |
| Full Idea: Frege's three main objections to radical formalism are that it cannot account for the application of mathematics, that it confuses a formal theory with its metatheory, and it cannot explain an infinite sequence. | |
| From: report of Gottlob Frege (Grundgesetze der Arithmetik 2 (Basic Laws) [1903], §86-137) by Michael Dummett - Frege philosophy of mathematics | |
| A reaction: The application is because we don't design maths randomly, but to be useful. The third objection might be dealt with by potential infinities (from formal rules). The second objection sounds promising. |
| 8751 | Only applicability raises arithmetic from a game to a science [Frege] |
| Full Idea: It is applicability alone which elevates arithmetic from a game to the rank of a science. | |
| From: Gottlob Frege (Grundgesetze der Arithmetik 2 (Basic Laws) [1903], §91), quoted by Stewart Shapiro - Thinking About Mathematics 6.1.2 | |
| A reaction: This is the basic objection to Formalism. It invites the question of why it is applicable, which platonists like Frege don't seem to answer (though Plato himself has reality modelled on the Forms). This is why I like structuralism. |
| 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. |
| 9891 | The first demand of logic is of a sharp boundary [Frege] |
| Full Idea: The first demand of logic is of a sharp boundary. | |
| From: Gottlob Frege (Grundgesetze der Arithmetik 2 (Basic Laws) [1903], §160), quoted by Michael Dummett - Frege philosophy of mathematics Ch.22 | |
| A reaction: Nothing I have read about vagueness has made me doubt Frege's view of this, although precisification might allow you to do logic with vague concepts without having to finally settle where the actual boundaries are. |
| 9389 | Vague membership of sets is possible if the set is defined by its concept, not its members [Rumfitt] |
| Full Idea: Vagueness in respect of membership is consistency with determinacy of the set's identity, so long as a set's identity is taken to consist, not in its having such-and-such members, but in its being the extension of a concept. | |
| From: Ian Rumfitt (The Logic of Boundaryless Concepts [2007], p.5) | |
| A reaction: I find this view of sets much more appealing than the one that identifies a set with its members. The empty set is less of a problem, as well as non-existents. Logicians prefer the extensional view because it is tidy. |
| 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) |
| 9890 | The modern account of real numbers detaches a ratio from its geometrical origins [Frege] |
| Full Idea: From geometry we retain the interpretation of a real number as a ratio of quantities or measurement-number; but in more recent times we detach it from geometrical quantities, and from all particular types of quantity. | |
| From: Gottlob Frege (Grundgesetze der Arithmetik 2 (Basic Laws) [1903], §159), quoted by Michael Dummett - Frege philosophy of mathematics | |
| A reaction: Dummett glosses the 'recent' version as by Cantor and Dedekind in 1872. This use of 'detach' seems to me startlingly like the sort of psychological abstractionism which Frege was so desperate to avoid. |
| 11846 | If we abstract the difference between two houses, they don't become the same house [Frege] |
| Full Idea: If abstracting from the difference between my house and my neighbour's, I were to regard both houses as mine, the defect of the abstraction would soon be made clear. It may, though, be possible to obtain a concept by means of abstraction... | |
| From: Gottlob Frege (Grundgesetze der Arithmetik 2 (Basic Laws) [1903], §99) | |
| A reaction: Note the important concession at the end, which shows Frege could never deny the abstraction process, despite all the modern protests by Geach and Dummett that he totally rejected it. |
| 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) |