21 ideas
| 10807 | Mathematics reduces to set theory, which reduces, with some mereology, to the singleton function [Lewis] |
| Full Idea: It is generally accepted that mathematics reduces to set theory, and I argue that set theory in turn reduces, with some aid of mereology, to the theory of the singleton function. | |
| From: David Lewis (Mathematics is Megethology [1993], p.03) |
| 10809 | We can accept the null set, but not a null class, a class lacking members [Lewis] |
| Full Idea: In my usage of 'class', there is no such things as the null class. I don't mind calling some memberless thing - some individual - the null set. But that doesn't make it a memberless class. Rather, that makes it a 'set' that is not a class. | |
| From: David Lewis (Mathematics is Megethology [1993], p.05) | |
| A reaction: Lewis calls this usage 'idiosyncratic', but it strikes me as excellent. Set theorists can have their vital null class, and sensible people can be left to say, with Lewis, that classes of things must have members. |
| 10811 | The null set plays the role of last resort, for class abstracts and for existence [Lewis] |
| Full Idea: The null set serves two useful purposes. It is a denotation of last resort for class abstracts that denote no nonempty class. And it is an individual of last resort: we can count on its existence, and fearlessly build the hierarchy of sets from it. | |
| From: David Lewis (Mathematics is Megethology [1993], p.09) | |
| A reaction: This passage assuages my major reservation about the existence of the null set, but at the expense of confirming that it must be taken as an entirely fictional entity. |
| 10812 | The null set is not a little speck of sheer nothingness, a black hole in Reality [Lewis] |
| Full Idea: Should we accept the null set as a most extraordinary individual, a little speck of sheer nothingness, a sort of black hole in the fabric of Reality itself? Not that either, I think. | |
| From: David Lewis (Mathematics is Megethology [1993], p.09) | |
| A reaction: Correct! |
| 10813 | What on earth is the relationship between a singleton and an element? [Lewis] |
| Full Idea: A new student of set theory has just one thing, the element, and he has another single thing, the singleton, and not the slightest guidance about what one thing has to do with the other. | |
| From: David Lewis (Mathematics is Megethology [1993], p.12) |
| 10814 | Are all singletons exact intrinsic duplicates? [Lewis] |
| Full Idea: Are all singletons exact intrinsic duplicates? | |
| From: David Lewis (Mathematics is Megethology [1993], p.13) |
| 10806 | Megethology is the result of adding plural quantification to mereology [Lewis] |
| Full Idea: Megethology is the result of adding plural quantification, as advocated by George Boolos, to the language of mereology. | |
| From: David Lewis (Mathematics is Megethology [1993], p.03) |
| 10816 | We can use mereology to simulate quantification over relations [Lewis] |
| Full Idea: We can simulate quantification over relations using megethology. Roughly, a quantifier over relations is a plural quantifier over things that encode ordered pairs by mereological means. | |
| From: David Lewis (Mathematics is Megethology [1993], p.18) | |
| A reaction: [He credits this idea to Burgess and Haven] The point is to avoid second-order logic, which quantifies over relations as ordered n-tuple sets. |
| 10808 | Mathematics is generalisations about singleton functions [Lewis] |
| Full Idea: We can take the theory of singleton functions, and hence set theory, and hence mathematics, to consist of generalisations about all singleton functions. | |
| From: David Lewis (Mathematics is Megethology [1993], p.03) | |
| A reaction: At first glance this sounds like a fancy version of the somewhat discredited Greek idea that mathematics is built on the concept of a 'unit'. |
| 10815 | We don't need 'abstract structures' to have structural truths about successor functions [Lewis] |
| Full Idea: We needn't believe in 'abstract structures' to have general structural truths about all successor functions. | |
| From: David Lewis (Mathematics is Megethology [1993], p.16) |
| 10810 | I say that absolutely any things can have a mereological fusion [Lewis] |
| Full Idea: I accept the principle of Unrestricted Composition: whenever there are some things, no matter how many or how unrelated or how disparate in character they may be, they have a mereological fusion. ...The trout-turkey is part fish and part fowl. | |
| From: David Lewis (Mathematics is Megethology [1993], p.07) | |
| A reaction: This nicely ducks the question of when things form natural wholes and when they don't, but I would have thought that that might be one of the central issues of metaphysicals, so I think I'll give Lewis's principle a miss. |
| 20298 | The traditional a priori is justified without experience; post-Quine it became unrevisable by experience [Rey] |
| Full Idea: Where Kant and others had traditionally assumed that the a priori concerned beliefs 'justifiable independently of experience', Quine and others of the time came to regard it as beliefs 'unrevisable in the light of experience'. | |
| From: Georges Rey (The Analytic/Synthetic Distinction [2013], 3.7) | |
| A reaction: That throws a rather striking light on Quine's project. Of course, if the a priori is also necessary, then it has to be unrevisable. But is a bachelor necessarily an unmarried man? It is not necessary that 'bachelor' has a fixed meaning. |
| 20300 | Externalist synonymy is there being a correct link to the same external phenomena [Rey] |
| Full Idea: Externalists are typically committed to counting expressions as 'synonymous' if they happen to be linked in the right way to the same external phenomena, even if a thinker couldn't realise that they are by reflection alone. | |
| From: Georges Rey (The Analytic/Synthetic Distinction [2013], 4.2) | |
| A reaction: [He cites Fodor] Externalists always try to link to concrete things in the world, but most of our talk is full of generalities, abstractions and fiction which don't link directly to anything. |
| 20294 | 'Married' does not 'contain' its symmetry, nor 'bigger than' its transitivity [Rey] |
| Full Idea: If Bob is married to Sue, then Sue is married to Bob. If x bigger than y, and y bigger than z, x is bigger than z. The symmetry of 'marriage' or transitivity of 'bigger than' are not obviously 'contained in' the corresponding thoughts. | |
| From: Georges Rey (The Analytic/Synthetic Distinction [2013], 1.2) | |
| A reaction: [Also 'if something is red, then it is coloured'] This is a Fregean criticism of Kant. It is not so much that Kant was wrong, as that the concept of analyticity is seen to have a much wider application than Kant realised. Especially in mathematics. |
| 20293 | Analytic judgements can't be explained by contradiction, since that is what is assumed [Rey] |
| Full Idea: Rejecting 'a married bachelor' as contradictory would seem to have no justification other than the claim that 'All bachelors are unmarried is analytic, and so cannot serve to justify or explain that claim. | |
| From: Georges Rey (The Analytic/Synthetic Distinction [2013], 1.2) | |
| A reaction: Rey is discussing Frege's objection to Kant (who tried to prove the necessity of analytic judgements, on the basis of the denial being a contradiction). |
| 20297 | Analytic statements are undeniable (because of meaning), rather than unrevisable [Rey] |
| Full Idea: What's peculiar about the analytic is that denying it seem unintelligible. Far from unrevisability explaining analyticity, it seems to be analyticitiy that explains unrevisability; we only balk at denying unmarried bachelors because that's what it means! | |
| From: Georges Rey (The Analytic/Synthetic Distinction [2013], 3.7) | |
| A reaction: This is a criticism of Quine, who attacked analyticity when it is understood as unrevisability. Obviously we could revise the concept of 'bachelor', if our marriage customs changed a lot. Rey seems right here. |
| 20301 | The meaning properties of a term are those which explain how the term is typically used [Rey] |
| Full Idea: It may be that the meaning properties of a term are the ones that play a basic explanatory role with regard to the use of the term generally, the ones in virtue ultimately of which a term is used with that meaning. | |
| From: Georges Rey (The Analytic/Synthetic Distinction [2013], 4.3) | |
| A reaction: [He cites Devitt 1996, 2002, and Horwich 1998, 2005) I spring to philosophical life whenever I see the word 'explanatory', because that is the point of the whole game. They are pointing to the essence of the concept (which is explanatory, say I). |
| 20302 | An intrinsic language faculty may fix what is meaningful (as well as grammatical) [Rey] |
| Full Idea: The existence of a separate language faculty may be an odd but psychologically real fact about us, and it may thereby supply a real basis for commitments about not only what is or is not grammatical, but about what is a matter of natural language meaning. | |
| From: Georges Rey (The Analytic/Synthetic Distinction [2013], 4.4) | |
| A reaction: This is the Chomskyan view of analytic sentences. An example from Chomsky (1977:142) is the semantic relationships of persuade, intend and believe. It's hard to see how the secret faculty on its own could do the job. Consensus is needed. |
| 20303 | Research throws doubts on the claimed intuitions which support analyticity [Rey] |
| Full Idea: The movement of 'experimental philosophy' has pointed to evidence of considerable malleability of subject's 'intuitions' with regard to the standard kinds of thought experiments on which defenses of analytic claims typically rely. | |
| From: Georges Rey (The Analytic/Synthetic Distinction [2013], 4.4) | |
| A reaction: See Cappelen's interesting attack on the idea that philosophy relies on intuitions, and hence his attack on experimental philosophy. Our consensus on ordinary English usage hardly qualifies as somewhat vague 'intuitions'. |
| 20299 | If we claim direct insight to what is analytic, how do we know it is not sub-consciously empirical? [Rey] |
| Full Idea: How in the end are we going to distinguish claims or the analytic as 'rational insight', 'primitive compulsion', inferential practice or folk belief from merely some deeply held empirical conviction, indeed, from mere dogma. | |
| From: Georges Rey (The Analytic/Synthetic Distinction [2013], 4.1) | |
| A reaction: This is Rey's summary of the persisting Quinean challenge to analytic truths, in the face of a set of replies, summarised by the various phrases here. So do we reject a dogma of empiricism, by asserting dogmatic empiricism? |
| 9425 | Lewis later proposed the axioms at the intersection of the best theories (which may be few) [Mumford on Lewis] |
| Full Idea: Later Lewis said we must choose between the intersection of the axioms of the tied best systems. He chose for laws the axioms that are in all the tied systems (but then there may be few or no axioms in the intersection). | |
| From: comment on David Lewis (Subjectivist's Guide to Objective Chance [1980], p.124) by Stephen Mumford - Laws in Nature |