24 ideas
| 15924 | Predicative definitions are acceptable in mathematics if they distinguish objects, rather than creating them? [Zermelo, by Lavine] |
| Full Idea: On Zermelo's view, predicative definitions are not only indispensable to mathematics, but they are unobjectionable since they do not create the objects they define, but merely distinguish them from other objects. | |
| From: report of Ernst Zermelo (Investigations in the Foundations of Set Theory I [1908]) by Shaughan Lavine - Understanding the Infinite V.1 | |
| A reaction: This seems to have an underlying platonism, that there are hitherto undefined 'objects' lying around awaiting the honour of being defined. Hm. |
| 17608 | We take set theory as given, and retain everything valuable, while avoiding contradictions [Zermelo] |
| Full Idea: Starting from set theory as it is historically given ...we must, on the one hand, restrict these principles sufficiently to exclude as contradiction and, on the other, take them sufficiently wide to retain all that is valuable in this theory. | |
| From: Ernst Zermelo (Investigations in the Foundations of Set Theory I [1908], Intro) | |
| A reaction: Maddy calls this the one-step-back-from-disaster rule of thumb. Zermelo explicitly mentions the 'Russell antinomy' that blocked Frege's approach to sets. |
| 17607 | Set theory investigates number, order and function, showing logical foundations for mathematics [Zermelo] |
| Full Idea: Set theory is that branch whose task is to investigate mathematically the fundamental notions 'number', 'order', and 'function', taking them in their pristine, simple form, and to develop thereby the logical foundations of all of arithmetic and analysis. | |
| From: Ernst Zermelo (Investigations in the Foundations of Set Theory I [1908], Intro) | |
| A reaction: At this point Zermelo seems to be a logicist. Right from the start set theory was meant to be foundational to mathematics, and not just a study of the logic of collections. |
| 10870 | ZFC: Existence, Extension, Specification, Pairing, Unions, Powers, Infinity, Choice [Zermelo, by Clegg] |
| Full Idea: Zermelo-Fraenkel axioms: Existence (at least one set); Extension (same elements, same set); Specification (a condition creates a new set); Pairing (two sets make a set); Unions; Powers (all subsets make a set); Infinity (set of successors); Choice | |
| From: report of Ernst Zermelo (Investigations in the Foundations of Set Theory I [1908]) by Brian Clegg - Infinity: Quest to Think the Unthinkable Ch.15 |
| 13012 | Zermelo published his axioms in 1908, to secure a controversial proof [Zermelo, by Maddy] |
| Full Idea: Zermelo proposed his listed of assumptions (including the controversial Axiom of Choice) in 1908, in order to secure his controversial proof of Cantor's claim that ' we can always bring any well-defined set into the form of a well-ordered set'. | |
| From: report of Ernst Zermelo (Investigations in the Foundations of Set Theory I [1908]) by Penelope Maddy - Believing the Axioms I §1 | |
| A reaction: This is interesting because it sometimes looks as if axiom systems are just a way of tidying things up. Presumably it is essential to get people to accept the axioms in their own right, the 'old-fashioned' approach that they be self-evident. |
| 17609 | Set theory can be reduced to a few definitions and seven independent axioms [Zermelo] |
| Full Idea: I intend to show how the entire theory created by Cantor and Dedekind can be reduced to a few definitions and seven principles, or axioms, which appear to be mutually independent. | |
| From: Ernst Zermelo (Investigations in the Foundations of Set Theory I [1908], Intro) | |
| A reaction: The number of axioms crept up to nine or ten in subsequent years. The point of axioms is maximum reduction and independence from one another. He says nothing about self-evidence (though Boolos claimed a degree of that). |
| 13017 | Zermelo introduced Pairing in 1930, and it seems fairly obvious [Zermelo, by Maddy] |
| Full Idea: Zermelo's Pairing Axiom superseded (in 1930) his original 1908 Axiom of Elementary Sets. Like Union, its only justification seems to rest on 'limitations of size' and on the 'iterative conception'. | |
| From: report of Ernst Zermelo (Investigations in the Foundations of Set Theory I [1908]) by Penelope Maddy - Believing the Axioms I §1.3 | |
| A reaction: Maddy says of this and Union, that they seem fairly obvious, but that their justification is of prime importance, if we are to understand what the axioms should be. |
| 13015 | Zermelo used Foundation to block paradox, but then decided that only Separation was needed [Zermelo, by Maddy] |
| Full Idea: Zermelo used a weak form of the Axiom of Foundation to block Russell's paradox in 1906, but in 1908 felt that the form of his Separation Axiom was enough by itself, and left the earlier axiom off his published list. | |
| From: report of Ernst Zermelo (Investigations in the Foundations of Set Theory I [1908]) by Penelope Maddy - Believing the Axioms I §1.2 | |
| A reaction: Foundation turns out to be fairly controversial. Barwise actually proposes Anti-Foundation as an axiom. Foundation seems to be the rock upon which the iterative view of sets is built. Foundation blocks infinite descending chains of sets, and circularity. |
| 13020 | The Axiom of Separation requires set generation up to one step back from contradiction [Zermelo, by Maddy] |
| Full Idea: The most characteristic Zermelo axiom is Separation, guided by a new rule of thumb: 'one step back from disaster' - principles of set generation should be as strong as possible short of contradiction. | |
| From: report of Ernst Zermelo (Investigations in the Foundations of Set Theory I [1908]) by Penelope Maddy - Believing the Axioms I §1.4 | |
| A reaction: Why is there an underlying assumption that we must have as many sets as possible? We are then tempted to abolish axioms like Foundation, so that we can have even more sets! |
| 13486 | Not every predicate has an extension, but Separation picks the members that satisfy a predicate [Zermelo, by Hart,WD] |
| Full Idea: Zermelo assumes that not every predicate has an extension but rather that given a set we may separate out from it those of its members satisfying the predicate. This is called 'separation' (Aussonderung). | |
| From: report of Ernst Zermelo (Investigations in the Foundations of Set Theory I [1908]) by William D. Hart - The Evolution of Logic 3 |
| 13487 | In ZF, the Burali-Forti Paradox proves that there is no set of all ordinals [Zermelo, by Hart,WD] |
| Full Idea: In Zermelo's set theory, the Burali-Forti Paradox becomes a proof that there is no set of all ordinals (so 'is an ordinal' has no extension). | |
| From: report of Ernst Zermelo (Investigations in the Foundations of Set Theory I [1908]) by William D. Hart - The Evolution of Logic 3 |
| 18178 | For Zermelo the successor of n is {n} (rather than n U {n}) [Zermelo, by Maddy] |
| Full Idea: For Zermelo the successor of n is {n} (rather than Von Neumann's successor, which is n U {n}). | |
| From: report of Ernst Zermelo (Investigations in the Foundations of Set Theory I [1908]) by Penelope Maddy - Naturalism in Mathematics I.2 n8 | |
| A reaction: I could ask some naive questions about the comparison of these two, but I am too shy about revealing my ignorance. |
| 13027 | Zermelo believed, and Von Neumann seemed to confirm, that numbers are sets [Zermelo, by Maddy] |
| Full Idea: Zermelo was a reductionist, and believed that theorems purportedly about numbers (cardinal or ordinal) are really about sets, and since Von Neumann's definitions of ordinals and cardinals as sets, this has become common doctrine. | |
| From: report of Ernst Zermelo (Investigations in the Foundations of Set Theory I [1908]) by Penelope Maddy - Believing the Axioms I §1.8 | |
| A reaction: Frege has a more sophisticated take on this approach. It may just be an updating of the Greek idea that arithmetic is about treating many things as a unit. A set bestows an identity on a group, and that is all that is needed. |
| 9627 | Different versions of set theory result in different underlying structures for numbers [Zermelo, by Brown,JR] |
| Full Idea: In Zermelo's set-theoretic definition of number, 2 is a member of 3, but not a member of 4; in Von Neumann's definition every number is a member of every larger number. This means they have two different structures. | |
| From: report of Ernst Zermelo (Investigations in the Foundations of Set Theory I [1908]) by James Robert Brown - Philosophy of Mathematics Ch. 4 | |
| A reaction: This refers back to the dilemma highlighted by Benacerraf, which was supposed to be the motivation for structuralism. My intuition says that the best answer is that they are both wrong. In a pattern, the nodes aren't 'members' of one another. |
| 7903 | The six perfections are giving, morality, patience, vigour, meditation, and wisdom [Nagarjuna] |
| Full Idea: The six perfections are of giving, morality, patience, vigour, meditation, and wisdom. | |
| From: Nagarjuna (Mahaprajnaparamitashastra [c.120], 88) | |
| A reaction: What is 'morality', if giving is not part of it? I like patience and vigour being two of the virtues, which immediately implies an Aristotelian mean (which is always what is 'appropriate'). |
| 23418 | Liberal state legitimacy is based on a belief in justice, not in some conception of the good life [Kymlicka] |
| Full Idea: For liberals the basis of state legitimacy is a shared sense of justice, not a shared conception of the good. | |
| From: Will Kymlicka (Community [1993], 'legitimacy') | |
| A reaction: For a liberal state to work, the citizens have to roughly believe in the core values of liberalism, which are primarily freedom and equality (and hence justice). |
| 23414 | Liberals say state intervention in culture restricts people's autonomy [Kymlicka] |
| Full Idea: According to liberal theory, a state which intervenes in the cultural market place to encourage any particular way of life restricts people's autonomy. | |
| From: Will Kymlicka (Community [1993], 'social') | |
| A reaction: The communitarian idea is that the state should intervene, in order to foster the best aspects of communal culture. The dangers are obvious, and can be seen in any totalitarian state. A gentle hand on the tiller, perhaps? Increase the options? |
| 23410 | Modern liberals see a community as simply a society which respects freedom and equality [Kymlicka] |
| Full Idea: Most contemporary liberal philosophers have little to say about the ideal of community. …It is often seen as derivative of liberty and equality - a society lives up to the ideal of community if its members are treated as free and equal persons. | |
| From: Will Kymlicka (Community [1993], 'Intro') | |
| A reaction: He cites Rawls as an example. This is the central idea which was attacked by modern communitarians. A collection of scattered self-seeking isolated individuals doesn't seem to amount to a healthy communal life. Maybe community needs further rights? |
| 23409 | Community can focus on class or citizenship or ethnicity or culture [Kymlicka] |
| Full Idea: In recent centuries the ideal of community has taken many forms, from class solidarity or shared citizenship to a common ethnic descent or cultural identity. | |
| From: Will Kymlicka (Community [1993], 'Intro') | |
| A reaction: Language and religion are not explicitly mentioned, but must be implied. Supporting a major sports team is also worth mentioning. |
| 23419 | Communitarianism struggles with excluded marginalised groups [Kymlicka] |
| Full Idea: The problem of the exclusion of historically marginalised groups is endemic to the communitarian project. | |
| From: Will Kymlicka (Community [1993], 'legitimacy') | |
| A reaction: Put simply, old-fashioned styles of community are probably impossible in large modern states, some with rather arbitrary borders. |
| 23413 | Feminism has shown that social roles are far from fixed (as communitarians tend to see them) [Kymlicka] |
| Full Idea: Communitarians say that some of our social roles must be regarded as fixed when planning our lives, …but the women's movement has shown how deeply entrenched social roles can be questioned and rejected. | |
| From: Will Kymlicka (Community [1993], 'Embedded') | |
| A reaction: True, but parents walking out on young children also shows that. The ideal must be some sort of balance. |
| 23415 | Participation aids the quest for the good life, but why should that be a state activity? [Kymlicka] |
| Full Idea: Communitarians rarely distinguish between collective activities and political activities. Shared participation aids intelligent decisions about the good life, but why should that be organised through the state, rather than by free individuals? | |
| From: Will Kymlicka (Community [1993], 'need') | |
| A reaction: Kylicka points out later that local groups can be very unintelligent or prejudiced. Modern media have changed that picture, because participation can be with geographically remote people. |
| 23411 | Communitarians see justice as primarily a community matter, rather than a principle [Kymlicka] |
| Full Idea: Communitarians believe either that community replaces the need for principles of justice, or that the community is either the source of such principles or should play a greater role in deciding their content. | |
| From: Will Kymlicka (Community [1993], 'Intro') | |
| A reaction: [compressed] The idea that a racist or chauvinist or puritanical or insular community should decide justice for all its members sounds horrible. It drives you to liberal individualism, just thinking about it. |
| 23412 | Justice resolves conflicts, but may also provoke them [Kymlicka] |
| Full Idea: Justice can help mediate conflicts, but it also tends to creat conflicts, and to decrease the natural expression of sociability. | |
| From: Will Kymlicka (Community [1993], 'limits') | |
| A reaction: [He is discussing Michael Sandel on liberalism] Family life might not go well if all of its members continually demanded justice for themselves as individuals. Maybe our concept of justice is too individualistic? Do we need a sense of 'group' justice? |