20 ideas
| 15544 | If what is actual might have been impossible, we need S4 modal logic [Armstrong, by Lewis] |
| Full Idea: Armstrong says what is actual (namely a certain roster of universals) might have been impossible. Hence his modal logic is S4, without the 'Brouwersche Axiom'. | |
| From: report of David M. Armstrong (A Theory of Universals [1978]) by David Lewis - Armstrong on combinatorial possibility 'The demand' | |
| A reaction: So p would imply possibly-not-possibly-p. |
| 9193 | ZF set theory has variables which range over sets, 'equals' and 'member', and extensionality [Dummett] |
| Full Idea: ZF set theory is a first-order axiomatization. Variables range over sets, there are no second-order variables, and primitive predicates are just 'equals' and 'member of'. The axiom of extensionality says sets with the same members are identical. | |
| From: Michael Dummett (The Philosophy of Mathematics [1998], 7) | |
| A reaction: If the eleven members of the cricket team are the same as the eleven members of the hockey team, is the cricket team the same as the hockey team? Our cricket team is better than our hockey team, so different predicates apply to them. |
| 9194 | The main alternative to ZF is one which includes looser classes as well as sets [Dummett] |
| Full Idea: The main alternative to ZF is two-sorted theories, with some variables ranging over classes. Classes have more generous existence assumptions: there is a universal class, containing all sets, and a class containing all ordinals. Classes are not members. | |
| From: Michael Dummett (The Philosophy of Mathematics [1998], 7.1.1) | |
| A reaction: My intuition is to prefer strict systems when it comes to logical theories. The whole point is precision. Otherwise we could just think about things, and skip all this difficult symbolic stuff. |
| 9195 | Intuitionists reject excluded middle, not for a third value, but for possibility of proof [Dummett] |
| Full Idea: It must not be concluded from the rejection of excluded middle that intuitionistic logic operates with three values: true, false, and neither true nor false. It does not make use of true and false, but only with a construction being a proof. | |
| From: Michael Dummett (The Philosophy of Mathematics [1998], 8.1) | |
| A reaction: This just sounds like verificationism to me, with all its problems. It seems to make speculative statements meaningless, which can't be right. Realism has lots of propositions which are assumed to be true or false, but also unknowable. |
| 9186 | First-order logic concerns objects; second-order adds properties, kinds, relations and functions [Dummett] |
| Full Idea: First-order logic is distinguished by generalizations (quantification) only over objects: second-order logic admits generalizations or quantification over properties or kinds of objects, and over relations between them, and functions defined over them. | |
| From: Michael Dummett (The Philosophy of Mathematics [1998], 3.1) | |
| A reaction: Second-order logic was introduced by Frege, but is (interestingly) rejected by Quine, because of the ontological commitments involved. I remain unconvinced that quantification entails ontological commitment, so I'm happy. |
| 9187 | Logical truths and inference are characterized either syntactically or semantically [Dummett] |
| Full Idea: There are two ways of characterizing logical truths and correct inference. Proof-theoretic or syntactic characterizations, if the formalization admits of proof or derivation; and model-theoretic or semantic versions, being true in all interpretations. | |
| From: Michael Dummett (The Philosophy of Mathematics [1998], 3.1) | |
| A reaction: Dummett calls this distinction 'fundamental'. The second one involves truth, and hence meaning, where the first one just responds to rules. ..But how can you have a notion of correctly following a rule, without a notion of truth? |
| 9191 | Ordinals seem more basic than cardinals, since we count objects in sequence [Dummett] |
| Full Idea: It can be argued that the notion of ordinal numbers is more fundamental than that of cardinals. To count objects, we must count them in sequence. ..The theory of ordinals forms the substratum of Cantor's theory of cardinals. | |
| From: Michael Dummett (The Philosophy of Mathematics [1998], 5) | |
| A reaction: Depends what you mean by 'fundamental'. I would take cardinality to be psychologically prior ('that is a lot of sheep'). You can't order people by height without first acquiring some people with differing heights. I vote for cardinals. |
| 9192 | The number 4 has different positions in the naturals and the wholes, with the same structure [Dummett] |
| Full Idea: The number 4 cannot be characterized solely by its position in a system, because it has different positions in the system of natural numbers and that of the positive whole numbers, whereas these systems have the very same structure. | |
| From: Michael Dummett (The Philosophy of Mathematics [1998], 6.1) | |
| A reaction: Dummett seems to think this is fairly decisive against structuralism. There is also the structure of the real numbers. We will solve this by saying that the wholes are abstracted from the naturals, which are abstracted from the reals. Job done. |
| 7024 | Properties are universals, which are always instantiated [Armstrong, by Heil] |
| Full Idea: Armstrong takes properties to be universals, and believes there are no 'uninstantiated' universals. | |
| From: report of David M. Armstrong (A Theory of Universals [1978]) by John Heil - From an Ontological Point of View §9.3 | |
| A reaction: At first glance this, like many theories of universals, seems to invite Ockham's Razor. If they are always instantiated, perhaps we should perhaps just try to talk about the instantiations (i.e. tropes), and skip the universal? |
| 9478 | Even if all properties are categorical, they may be denoted by dispositional predicates [Armstrong, by Bird] |
| Full Idea: Armstrong says all properties are categorical, but a dispositional predicate may denote such a property; the dispositional predicate denotes the categorical property in virtue of the dispositional role it happens, contingently, to play in this world. | |
| From: report of David M. Armstrong (A Theory of Universals [1978]) by Alexander Bird - Nature's Metaphysics 3.1 | |
| A reaction: I favour the fundamentality of the dispositional rather than the categorical. The world consists of powers, and we find ourselves amidst their categorical expressions. I could be persuaded otherwise, though! |
| 10729 | Universals explain resemblance and causal power [Armstrong, by Oliver] |
| Full Idea: Armstrong thinks universals play two roles, namely grounding objective resemblances and grounding causal powers. | |
| From: report of David M. Armstrong (A Theory of Universals [1978]) by Alex Oliver - The Metaphysics of Properties 11 | |
| A reaction: Personally I don't think universals explain anything at all. They just add another layer of confusion to a difficult problem. Oliver objects that this seems a priori, contrary to Armstrong's principle in Idea 10728. |
| 4031 | It doesn't follow that because there is a predicate there must therefore exist a property [Armstrong] |
| Full Idea: I suggest that we reject the notion that just because the predicate 'red' applies to an open class of particulars, therefore there must be a property, redness. | |
| From: David M. Armstrong (A Theory of Universals [1978], p.8), quoted by DH Mellor / A Oliver - Introduction to 'Properties' §6 | |
| A reaction: At last someone sensible (an Australian) rebuts that absurd idea that our ontology is entirely a feature of our language |
| 10024 | The type-token distinction is the universal-particular distinction [Armstrong, by Hodes] |
| Full Idea: Armstrong conflates the type-token distinction with that between universals and particulars. | |
| From: report of David M. Armstrong (A Theory of Universals [1978], xiii,16/17) by Harold Hodes - Logicism and Ontological Commits. of Arithmetic 147 n23 | |
| A reaction: This seems quite reasonable, even if you don’t believe in the reality of universals. I'm beginning to think we should just use the term 'general' instead of 'universal'. 'Type' also seems to correspond to 'set', with the 'token' as the 'member'. |
| 10728 | A thing's self-identity can't be a universal, since we can know it a priori [Armstrong, by Oliver] |
| Full Idea: Armstrong says that if it can be proved a priori that a thing falls under a certain universal, then there is no such universal - and hence there is no universal of a thing being identical with itself. | |
| From: report of David M. Armstrong (A Theory of Universals [1978], II p.11) by Alex Oliver - The Metaphysics of Properties 11 | |
| A reaction: This is a distinctively Armstrongian view, based on his belief that universals must be instantiated, and must be discoverable a posteriori, as part of science. I'm baffled by self-identity, but I don't think this argument does the job. |
| 21515 | Incoherence may be more important for enquiry than coherence [Olsson] |
| Full Idea: While coherence may lack the positive role many have assigned to it, ...incoherence plays an important negative role in our enquiries. | |
| From: Erik J. Olsson (Against Coherence [2005], 10.1) | |
| A reaction: [He cites Peirce as the main source for this idea] We can hardly by deeply impressed by incoherence if we have no sense of coherence. Incoherence is just one of many markers for theory failure. Missing the target, bad concepts... |
| 21514 | Coherence is the capacity to answer objections [Olsson] |
| Full Idea: According to Lehrer, coherence should be understood in terms of the capacity to answer objections. | |
| From: Erik J. Olsson (Against Coherence [2005], 9) | |
| A reaction: [Keith Lehrer 1990] We can connect this with the Greek requirement of being able to give an account [logos], which is the hallmark of understanding. I take coherence to be the best method of achieving understanding. Any understanding meets Lehrer's test. |
| 21496 | Mere agreement of testimonies is not enough to make truth very likely [Olsson] |
| Full Idea: Far from guaranteeing a high likelihood of truth by itself, testimonial agreement can apparently do so only if the circumstances are favourable as regards independence, prior probability, and individual credibility. | |
| From: Erik J. Olsson (Against Coherence [2005], 1) | |
| A reaction: This is Olson's main thesis. His targets are C.I.Lewis and Bonjour, who hoped that a mere consensus of evidence would increase verisimilitude. I don't see a problem for coherence in general, since his favourable circumstances are part of it. |
| 21499 | Coherence is only needed if the information sources are not fully reliable [Olsson] |
| Full Idea: An enquirer who is fortunate enough to have at his or her disposal fully reliable information sources has no use for coherence, the need for which arises only in the context of less than fully reliable informations sources. | |
| From: Erik J. Olsson (Against Coherence [2005], 2.6.2) | |
| A reaction: I take this to be entirely false. How do you assess reliability? 'I've seen it with my own eyes'. Why trust your eyes? In what visibility conditions do you begin to doubt your eyes? Why do rational people mistrust their intuitions? |
| 21502 | A purely coherent theory cannot be true of the world without some contact with the world [Olsson] |
| Full Idea: The Input Objection says a pure coherence theory would seem to allow that a system of beliefs be justified in spite of being utterly out of contact with the world it purports to describe, so long as it is, to a sufficient extent, coherent. | |
| From: Erik J. Olsson (Against Coherence [2005], 4.1) | |
| A reaction: Olson seems impressed by this objection, but I don't see how a system could be coherently about the world if it had no known contact with the world. Olson seems to ignore meta-coherence, which evaluates the status of the system being studied. |
| 21512 | Extending a system makes it less probable, so extending coherence can't make it more probable [Olsson] |
| Full Idea: Any non-trivial extension of a belief system is less probable than the original system, but there are extensions that are more coherent than the original system. Hence more coherence does not imply a higher probability. | |
| From: Erik J. Olsson (Against Coherence [2005], 6.4) | |
| A reaction: [Olson cites Klein and Warfield 1994; compressed] The example rightly says the extension could have high internal coherence, but not whether the extension is coherent with the system being extended. |