46 ideas
| 10482 | The logic of ZF is classical first-order predicate logic with identity [Boolos] |
| Full Idea: The logic of ZF Set Theory is classical first-order predicate logic with identity. | |
| From: George Boolos (Must We Believe in Set Theory? [1997], p.121) | |
| A reaction: This logic seems to be unable to deal with very large cardinals, precisely those that are implied by set theory, so there is some sort of major problem hovering here. Boolos is fairly neutral. |
| 10492 | A few axioms of set theory 'force themselves on us', but most of them don't [Boolos] |
| Full Idea: Maybe the axioms of extensionality and the pair set axiom 'force themselves on us' (Gödel's phrase), but I am not convinced about the axioms of infinity, union, power or replacement. | |
| From: George Boolos (Must We Believe in Set Theory? [1997], p.130) | |
| A reaction: Boolos is perfectly happy with basic set theory, but rather dubious when very large cardinals come into the picture. |
| 18192 | Do the Replacement Axioms exceed the iterative conception of sets? [Boolos, by Maddy] |
| Full Idea: For Boolos, the Replacement Axioms go beyond the iterative conception. | |
| From: report of George Boolos (The iterative conception of Set [1971]) by Penelope Maddy - Naturalism in Mathematics I.3 |
| 7785 | The use of plurals doesn't commit us to sets; there do not exist individuals and collections [Boolos] |
| Full Idea: We should abandon the idea that the use of plural forms commits us to the existence of sets/classes… Entities are not to be multiplied beyond necessity. There are not two sorts of things in the world, individuals and collections. | |
| From: George Boolos (To be is to be the value of a variable.. [1984]), quoted by Henry Laycock - Object | |
| A reaction: The problem of quantifying over sets is notoriously difficult. Try http://plato.stanford.edu/entries/object/index.html. |
| 10485 | Naïve sets are inconsistent: there is no set for things that do not belong to themselves [Boolos] |
| Full Idea: The naïve view of set theory (that any zero or more things form a set) is natural, but inconsistent: the things that do not belong to themselves are some things that do not form a set. | |
| From: George Boolos (Must We Believe in Set Theory? [1997], p.127) | |
| A reaction: As clear a summary of Russell's Paradox as you could ever hope for. |
| 10484 | The iterative conception says sets are formed at stages; some are 'earlier', and must be formed first [Boolos] |
| Full Idea: According to the iterative conception, every set is formed at some stage. There is a relation among stages, 'earlier than', which is transitive. A set is formed at a stage if and only if its members are all formed before that stage. | |
| From: George Boolos (Must We Believe in Set Theory? [1997], p.126) | |
| A reaction: He gives examples of the early stages, and says the conception is supposed to 'justify' Zermelo set theory. It is also supposed to make the axioms 'natural', rather than just being selected for convenience. And it is consistent. |
| 13547 | Limitation of Size is weak (Fs only collect is something the same size does) or strong (fewer Fs than objects) [Boolos, by Potter] |
| Full Idea: Weak Limitation of Size: If there are no more Fs than Gs and the Gs form a collection, then Fs form a collection. Strong Limitation of Size: A property F fails to be collectivising iff there are as many Fs as there are objects. | |
| From: report of George Boolos (Iteration Again [1989]) by Michael Potter - Set Theory and Its Philosophy 13.5 |
| 10699 | Does a bowl of Cheerios contain all its sets and subsets? [Boolos] |
| Full Idea: Is there, in addition to the 200 Cheerios in a bowl, also a set of them all? And what about the vast number of subsets of Cheerios? It is haywire to think that when you have some Cheerios you are eating a set. What you are doing is: eating the Cheerios. | |
| From: George Boolos (To be is to be the value of a variable.. [1984], p.72) | |
| A reaction: In my case Boolos is preaching to the converted. I am particularly bewildered by someone (i.e. Quine) who believes that innumerable sets exist while 'having a taste for desert landscapes' in their ontology. |
| 14249 | Boolos reinterprets second-order logic as plural logic [Boolos, by Oliver/Smiley] |
| Full Idea: Boolos's conception of plural logic is as a reinterpretation of second-order logic. | |
| From: report of George Boolos (On Second-Order Logic [1975]) by Oliver,A/Smiley,T - What are Sets and What are they For? n5 | |
| A reaction: Oliver and Smiley don't accept this view, and champion plural reference differently (as, I think, some kind of metalinguistic device?). |
| 10225 | Monadic second-order logic might be understood in terms of plural quantifiers [Boolos, by Shapiro] |
| Full Idea: Boolos has proposed an alternative understanding of monadic, second-order logic, in terms of plural quantifiers, which many philosophers have found attractive. | |
| From: report of George Boolos (To be is to be the value of a variable.. [1984]) by Stewart Shapiro - Philosophy of Mathematics 3.5 |
| 10830 | Second-order logic metatheory is set-theoretic, and second-order validity has set-theoretic problems [Boolos] |
| Full Idea: The metatheory of second-order logic is hopelessly set-theoretic, and the notion of second-order validity possesses many if not all of the epistemic debilities of the notion of set-theoretic truth. | |
| From: George Boolos (On Second-Order Logic [1975], p.45) | |
| A reaction: Epistemic problems arise when a logic is incomplete, because some of the so-called truths cannot be proved, and hence may be unreachable. This idea indicates Boolos's motivation for developing a theory of plural quantification. |
| 10736 | Boolos showed how plural quantifiers can interpret monadic second-order logic [Boolos, by Linnebo] |
| Full Idea: In an indisputable technical result, Boolos showed how plural quantifiers can be used to interpret monadic second-order logic. | |
| From: report of George Boolos (To be is to be the value of a variable.. [1984], Intro) by Øystein Linnebo - Plural Quantification Exposed Intro |
| 10780 | Any sentence of monadic second-order logic can be translated into plural first-order logic [Boolos, by Linnebo] |
| Full Idea: Boolos discovered that any sentence of monadic second-order logic can be translated into plural first-order logic. | |
| From: report of George Boolos (To be is to be the value of a variable.. [1984], §1) by Øystein Linnebo - Plural Quantification Exposed p.74 |
| 10829 | A sentence can't be a truth of logic if it asserts the existence of certain sets [Boolos] |
| Full Idea: One may be of the opinion that no sentence ought to be considered as a truth of logic if, no matter how it is interpreted, it asserts that there are sets of certain sorts. | |
| From: George Boolos (On Second-Order Logic [1975], p.44) | |
| A reaction: My intuition is that in no way should any proper logic assert the existence of anything at all. Presumably interpretations can assert the existence of numbers or sets, but we should be able to identify something which is 'pure' logic. Natural deduction? |
| 10697 | Identity is clearly a logical concept, and greatly enhances predicate calculus [Boolos] |
| Full Idea: Indispensable to cross-reference, lacking distinctive content, and pervading thought and discourse, 'identity' is without question a logical concept. Adding it to predicate calculus significantly increases the number and variety of inferences possible. | |
| From: George Boolos (To be is to be the value of a variable.. [1984], p.54) | |
| A reaction: It is not at all clear to me that identity is a logical concept. Is 'existence' a logical concept? It seems to fit all of Boolos's criteria? I say that all he really means is that it is basic to thought, but I'm not sure it drives the reasoning process. |
| 10832 | '∀x x=x' only means 'everything is identical to itself' if the range of 'everything' is fixed [Boolos] |
| Full Idea: One may say that '∀x x=x' means 'everything is identical to itself', but one must realise that one's answer has a determinate sense only if the reference (range) of 'everything' is fixed. | |
| From: George Boolos (On Second-Order Logic [1975], p.46) | |
| A reaction: This is the problem now discussed in the recent book 'Absolute Generality', of whether one can quantify without specifying a fixed or limited domain. |
| 13671 | Second-order quantifiers are just like plural quantifiers in ordinary language, with no extra ontology [Boolos, by Shapiro] |
| Full Idea: Boolos proposes that second-order quantifiers be regarded as 'plural quantifiers' are in ordinary language, and has developed a semantics along those lines. In this way they introduce no new ontology. | |
| From: report of George Boolos (To be is to be the value of a variable.. [1984]) by Stewart Shapiro - Foundations without Foundationalism 7 n32 | |
| A reaction: This presumably has to treat simple predicates and relations as simply groups of objects, rather than having platonic existence, or something. |
| 10267 | We should understand second-order existential quantifiers as plural quantifiers [Boolos, by Shapiro] |
| Full Idea: Standard second-order existential quantifiers pick out a class or a property, but Boolos suggests that they be understood as a plural quantifier, like 'there are objects' or 'there are people'. | |
| From: report of George Boolos (To be is to be the value of a variable.. [1984]) by Stewart Shapiro - Philosophy of Mathematics 7.4 | |
| A reaction: This idea has potential application to mathematics, and Lewis (1991, 1993) 'invokes it to develop an eliminative structuralism' (Shapiro). |
| 10698 | Plural forms have no more ontological commitment than to first-order objects [Boolos] |
| Full Idea: Abandon the idea that use of plural forms must always be understood to commit one to the existence of sets of those things to which the corresponding singular forms apply. | |
| From: George Boolos (To be is to be the value of a variable.. [1984], p.66) | |
| A reaction: It seems to be an open question whether plural quantification is first- or second-order, but it looks as if it is a rewriting of the first-order. |
| 7806 | Boolos invented plural quantification [Boolos, by Benardete,JA] |
| Full Idea: Boolos virtually patented the new device of plural quantification. | |
| From: report of George Boolos (To be is to be the value of a variable.. [1984]) by José A. Benardete - Logic and Ontology | |
| A reaction: This would be 'there are some things such that...' |
| 10834 | Weak completeness: if it is valid, it is provable. Strong: it is provable from a set of sentences [Boolos] |
| Full Idea: A weak completeness theorem shows that a sentence is provable whenever it is valid; a strong theorem, that a sentence is provable from a set of sentences whenever it is a logical consequence of the set. | |
| From: George Boolos (On Second-Order Logic [1975], p.52) | |
| A reaction: So the weak version says |- φ → |= φ, and the strong versions says Γ |- φ → Γ |= φ. Presumably it is stronger if it can specify the source of the inference. |
| 13841 | Why should compactness be definitive of logic? [Boolos, by Hacking] |
| Full Idea: Boolos asks why on earth compactness, whatever its virtues, should be definitive of logic itself. | |
| From: report of George Boolos (On Second-Order Logic [1975]) by Ian Hacking - What is Logic? §13 |
| 10491 | Infinite natural numbers is as obvious as infinite sentences in English [Boolos] |
| Full Idea: The existence of infinitely many natural numbers seems to me no more troubling than that of infinitely many computer programs or sentences of English. There is, for example, no longest sentence, since any number of 'very's can be inserted. | |
| From: George Boolos (Must We Believe in Set Theory? [1997], p.129) | |
| A reaction: If you really resisted an infinity of natural numbers, presumably you would also resist an actual infinity of 'very's. The fact that it is unclear what could ever stop a process doesn't guarantee that the process is actually endless. |
| 10483 | Mathematics and science do not require very high orders of infinity [Boolos] |
| Full Idea: To the best of my knowledge nothing in mathematics or science requires the existence of very high orders of infinity. | |
| From: George Boolos (Must We Believe in Set Theory? [1997], p.122) | |
| A reaction: He is referring to particular high orders of infinity implied by set theory. Personally I want to wield Ockham's Razor. Is being implied by set theory a sufficient reason to accept such outrageous entities into our ontology? |
| 10833 | Many concepts can only be expressed by second-order logic [Boolos] |
| Full Idea: The notions of infinity and countability can be characterized by second-order sentences, though not by first-order sentences (as compactness and Skolem-Löwenheim theorems show), .. as well as well-ordering, progression, ancestral and identity. | |
| From: George Boolos (On Second-Order Logic [1975], p.48) |
| 10490 | Mathematics isn't surprising, given that we experience many objects as abstract [Boolos] |
| Full Idea: It is no surprise that we should be able to reason mathematically about many of the things we experience, for they are already 'abstract'. | |
| From: George Boolos (Must We Believe in Set Theory? [1997], p.129) | |
| A reaction: He has just given a list of exemplary abstract objects (Idea 10489), but I think there is a more interesting idea here - that our experience of actual physical objects is to some extent abstract, as soon as it is conceptualised. |
| 10700 | First- and second-order quantifiers are two ways of referring to the same things [Boolos] |
| Full Idea: Ontological commitment is carried by first-order quantifiers; a second-order quantifier needn't be taken to be a first-order quantifier in disguise, having special items, collections, as its range. They are two ways of referring to the same things. | |
| From: George Boolos (To be is to be the value of a variable.. [1984], p.72) | |
| A reaction: If second-order quantifiers are just a way of referring, then we can see first-order quantifiers that way too, so we could deny 'objects'. |
| 10488 | It is lunacy to think we only see ink-marks, and not word-types [Boolos] |
| Full Idea: It's a kind of lunacy to think that sound scientific philosophy demands that we think that we see ink-tracks but not words, i.e. word-types. | |
| From: George Boolos (Must We Believe in Set Theory? [1997], p.128) | |
| A reaction: This seems to link him with Armstrong's mockery of 'ostrich nominalism'. There seems to be some ambiguity with the word 'see' in this disagreement. When we look at very ancient scratches on stones, why don't we always 'see' if it is words? |
| 10487 | I am a fan of abstract objects, and confident of their existence [Boolos] |
| Full Idea: I am rather a fan of abstract objects, and confident of their existence. Smaller numbers, sets and functions don't offend my sense of reality. | |
| From: George Boolos (Must We Believe in Set Theory? [1997], p.128) | |
| A reaction: The great Boolos is rather hard to disagree with, but I disagree. Logicians love abstract objects, indeed they would almost be out of a job without them. It seems to me they smuggle them into our ontology by redefining either 'object' or 'exists'. |
| 10489 | We deal with abstract objects all the time: software, poems, mistakes, triangles.. [Boolos] |
| Full Idea: We twentieth century city dwellers deal with abstract objects all the time, such as bank balances, radio programs, software, newspaper articles, poems, mistakes, triangles. | |
| From: George Boolos (Must We Believe in Set Theory? [1997], p.129) | |
| A reaction: I find this claim to be totally question-begging, and typical of a logician. The word 'object' gets horribly stretched in these discussions. We can create concepts which have all the logical properties of objects. Maybe they just 'subsist'? |
| 3061 | Anaxarchus said that he was not even sure that he knew nothing [Anaxarchus, by Diog. Laertius] |
| Full Idea: Anaxarchus said that he was not even sure that he knew nothing. | |
| From: report of Anaxarchus (fragments/reports [c.340 BCE]) by Diogenes Laertius - Lives of Eminent Philosophers 09.10.1 |
| 6685 | 'Subjectivism' is an extension of relativism from the social group to the individual [Graham] |
| Full Idea: What is called 'subjectivism' is really just an extension of relativism from the level of the social group to the level of the individual. | |
| From: Gordon Graham (Eight Theories of Ethics [2004], Ch.1) | |
| A reaction: Personally I prefer to stick with 'relativism', at any level. 'Relative' is a two-place predicate, so we should always specify what is relative to what, unless it is obvious from context. Morality might be relative to God, for example. |
| 8693 | An 'abstraction principle' says two things are identical if they are 'equivalent' in some respect [Boolos] |
| Full Idea: Hume's Principle has a structure Boolos calls an 'abstraction principle'. Within the scope of two universal quantifiers, a biconditional connects an identity between two things and an equivalence relation. It says we don't care about other differences. | |
| From: George Boolos (Is Hume's Principle analytic? [1997]), quoted by Michèle Friend - Introducing the Philosophy of Mathematics 3.7 | |
| A reaction: This seems to be the traditional principle of abstraction by ignoring some properties, but dressed up in the clothes of formal logic. Frege tries to eliminate psychology, but Boolos implies that what we 'care about' is relevant. |
| 6699 | The chain of consequences may not be the same as the chain of responsibility [Graham] |
| Full Idea: From a utilitarian point of view, the error of Archduke Ferdinand's driver (he turned up a cul-de-sac) was the worst in history, ...but the chain of consequences may not be the same as the chain of responsibility. | |
| From: Gordon Graham (Eight Theories of Ethics [2004], Ch.7) | |
| A reaction: Can you cause something, and yet not be responsible for it? The driver was presumably fully conscious, rational and deliberate. He must share the responsibility for catastrophe, just as he shares in the causing of all the consequences. |
| 6698 | Negative consequences are very hard (and possibly impossible) to assess [Graham] |
| Full Idea: Negative consequences make the extension of the consequences of our actions indefinite, and this means that it is difficult to assess them; it may make it impossible, since there is now no clear sense to the idea of THE consequences of an action at all. | |
| From: Gordon Graham (Eight Theories of Ethics [2004], Ch.7) | |
| A reaction: The general slogan of 'Do your best' covers most objections to the calculation of consequences. It is no excuse for stealing a wallet that 'at least I wasn't committing genocide'. How easy were the alternative actions to do? |
| 6700 | We can't criticise people because of unforeseeable consequences [Graham] |
| Full Idea: It is unreasonable to say that people have acted badly because of consequences which were not merely unforeseen but unforeseeable. | |
| From: Gordon Graham (Eight Theories of Ethics [2004], Ch.7) | |
| A reaction: Interesting, and it sounds right. A key question in moral philosophy is how much effort people should make to assess the consequences of their actions. We must surely absolve them of the truly 'unforeseeable' consequence. |
| 6704 | Egoism submits to desires, but cannot help form them [Graham] |
| Full Idea: Egoism is inadequate as a guide to good living. Though it tells us what to do, given pre-existent desires, it cannot help us critically form those desires. | |
| From: Gordon Graham (Eight Theories of Ethics [2004], Ch.9) | |
| A reaction: A crucial point in morality. It also applies to utilitarianism (should I change my capacity for pleasure?), and virtue theory (how should I genetically engineer 'human nature'?). I think these problems push us towards Platonism. See Idea 4840. |
| 6701 | Rescue operations need spontaneous benevolence, not careful thought [Graham] |
| Full Idea: If more lives are to be saved in natural disasters, what is needed is spontaneity on the part of the rescuers, a willingness not to stop and think but to act spontaneously. | |
| From: Gordon Graham (Eight Theories of Ethics [2004], Ch.7) | |
| A reaction: This seems right, but must obviously be applied with caution, as when people are drowned attempting hopeless rescues. The most valuable person in an earthquake may be the thinker, not the digger. |
| 6693 | 'What if everybody did that?' rather misses the point as an objection to cheating [Graham] |
| Full Idea: I can object to your walking on the grass by asking 'What if everybody did that?', but the advantages of cheating depend upon the fact that most people don't cheat, so justifying my own cheating must involve special pleading. | |
| From: Gordon Graham (Eight Theories of Ethics [2004], Ch.6) | |
| A reaction: It is, of course, reasonable to ask 'What if everybody cheated?', but it is also reasonable to reply that 'the whole point of cheating is that it exploits the honesty of others'. This shows that Kant cannot simply demolish the 'free rider'. |
| 6691 | It is more plausible to say people can choose between values, than that they can create them [Graham] |
| Full Idea: To say that individuals are free to choose their own values is more naturally interpreted as meaning that they are free to choose between pre-existent values. | |
| From: Gordon Graham (Eight Theories of Ethics [2004], Ch.5) | |
| A reaction: Existentialism seems absurdly individualistic in its morality. Nietzsche was the best existentialist, who saw that most people have to be sheep. Strong personalities can promote or demote the old values on the great scale of what is good. |
| 6688 | Life is only absurd if you expected an explanation and none turns up [Graham] |
| Full Idea: If 'life is absurd' just means 'there is no logical explanation for human existence', we have no reason for anguish, unless we think there should be such an explanation. | |
| From: Gordon Graham (Eight Theories of Ethics [2004], Ch.5) | |
| A reaction: This is aimed at Kierkegaard and Camus. 'Absurd' certainly seems to be a relative notion, and we have nothing to compare life with. However, life does strike us as a bit odd sometimes, don't you think? |
| 6705 | Existentialism may transcend our nature, unlike eudaimonism [Graham] |
| Full Idea: It is the freedom to transcend our nature which eudaimonism seems to ignore and existentialism brings to the fore. | |
| From: Gordon Graham (Eight Theories of Ethics [2004], Ch.9) | |
| A reaction: It is wildly exciting to 'transcend our nature', and very dreary to polish up the nature which is given to us. In this I am a bit conservative. We should not go against the grain, but we shouldn't assume current living is the correct line of the grain. |
| 6690 | A standard problem for existentialism is the 'sincere Nazi' [Graham] |
| Full Idea: A standard problem for existentialism is the 'sincere Nazi'; there were undoubtedly some true believers, who saw in Nazism a creed that they wanted to believe, and who freely chose to endorse it. | |
| From: Gordon Graham (Eight Theories of Ethics [2004], Ch.5) | |
| A reaction: The failing of Nazis was that they were not good citizens. They might have been good members of a faction, but they were (in my opinion) poor citizens of Germany, and (obviously) appalling citizens of Europe. The objection to existentialism is good. |
| 6689 | The key to existentialism: the way you make choices is more important than what you choose [Graham] |
| Full Idea: The chief implication of existentialism is this: what you choose to do, how you choose to spend your life, is not as important as the way you choose it. | |
| From: Gordon Graham (Eight Theories of Ethics [2004], Ch.5) | |
| A reaction: While existentialists place emphasis on some notion of 'pure' choice, this is very close to the virtue theory idea that in a dilemma there may be several different choices which could all be rightly made by virtuous people. Integrity is a central virtue. |
| 6706 | The great religions are much more concerned with the religious life than with ethics [Graham] |
| Full Idea: The fact is that the great religions of the world are not principally concerned with ethics at all, but with the religious life for its own sake. ..The Sermon on the Mount, for example, is mainly concerned with how to pray and worship. | |
| From: Gordon Graham (Eight Theories of Ethics [2004], Ch.9) | |
| A reaction: This seems to me a highly significant point, given that most people nowadays seem to endorse religion precisely because they wish to endorse morality, and think religion is its essential underpinning. See Idea 336 for the core problem ('Euthyphro'). |
| 6709 | Western religion saves us from death; Eastern religion saves us from immortality [Graham] |
| Full Idea: For Western minds, religion entails the belief and hope that we will be saved from death and live forever, but the belief of Eastern religions is that we do live forever, and it is from this dreadful fate that we must look to spirituality to save us. | |
| From: Gordon Graham (Eight Theories of Ethics [2004], Ch.9) | |
| A reaction: Nice. I have certainly come to prefer the Eastern view, simply on the grounds that human beings have a limited capacity. I quite fancy three hundred years of healthy life, but after that I am sure that any potential I have will be used up. |