display all the ideas for this combination of philosophers
15 ideas
19053 | Logic would be more natural if negation only referred to predicates [Dummett] |
Full Idea: A better proposal for a formal logic closer to natural language would be one that had a negation-operator only for (simple) predicates. | |
From: Michael Dummett (Presupposition [1960], p.27) | |
A reaction: Dummett observes that classical formal logic was never intended to be close to natural language. Term logic does have that aim, but the meta-question is whether that end is desirable, and why. |
19060 | Truth-tables are dubious in some cases, and may be a bad way to explain connective meaning [Dummett] |
Full Idea: It is arguable whether two-valued truth tables give correct meanings for certain sentential operators, and even whether they constitute legitimate explanations of any possible sentential operators. | |
From: Michael Dummett (The Justification of Deduction [1973], p.294) | |
A reaction: See 'Many-valued logic' for examples of non-binary truth tables. Presumably logicians should aspire to make their semantics precise, as well as their syntax. |
5737 | Predicate logic has connectives, quantifiers, variables, predicates, equality, names and brackets [Melia] |
Full Idea: First-order predicate language has four connectives, two quantifiers, variables, predicates, equality, names, and brackets. | |
From: Joseph Melia (Modality [2003], Ch.2) | |
A reaction: Look up the reference for the details! The spirit of logic is seen in this basic framework, and the main interest is in the ontological commitment of the items on the list. The list is either known a priori, or it is merely conventional. |
16951 | It was realised that possible worlds covered all modal logics, if they had a structure [Dummett] |
Full Idea: The new discovery was that with a suitable structure imposed on the space of possible worlds, the Leibnizian idea would work for all modal logics. | |
From: Michael Dummett (Could There Be Unicorns? [1983], 1) |
5744 | First-order predicate calculus is extensional logic, but quantified modal logic is intensional (hence dubious) [Melia] |
Full Idea: First-order predicate calculus is an extensional logic, while quantified modal logic is intensional (which has grave problems of interpretation, according to Quine). | |
From: Joseph Melia (Modality [2003], Ch.3) | |
A reaction: The battle is over ontology. Quine wants the ontology to stick with the values of the variables (i.e. the items in the real world that are quantified over in the extension). The rival view arises from attempts to explain necessity and counterfactuals. |
16952 | If something is only possible relative to another possibility, the possibility relation is not transitive [Dummett] |
Full Idea: If T is only possible if S obtains, and S is possible but doesn't obtain, then T is only possible in the world where S obtains, but T is not possible in the actual world. It follows that the relation of relative possibility is not transitive. | |
From: Michael Dummett (Could There Be Unicorns? [1983], 1) | |
A reaction: [compressed] |
16953 | Relative possibility one way may be impossible coming back, so it isn't symmetrical [Dummett] |
Full Idea: If T is only possible if S obtains, T and S hold in the actual world, and S does not obtain in world v possible relative to the actual world, then the actual is not possible relative to v, since T holds in the actual. Accessibility can't be symmetrical. | |
From: Michael Dummett (Could There Be Unicorns? [1983], 1) |
16960 | If possibilitiy is relative, that might make accessibility non-transitive, and T the correct system [Dummett] |
Full Idea: If some world is 'a way the world might be considered to be if things were different in a certain respect', that might show that the accessibility relation should not be taken to be transitive, and we should have to adopt modal logic T. | |
From: Michael Dummett (Could There Be Unicorns? [1983], 8) | |
A reaction: He has already rejected symmetry from the relation, for reasons concerning relative identity. He is torn between T and S4, but rejects S5, and opts not to discuss it. |
16958 | In S4 the actual world has a special place [Dummett] |
Full Idea: In S4 logic the actual world is, in itself, special, not just from our point of view. | |
From: Michael Dummett (Could There Be Unicorns? [1983], 8) | |
A reaction: S4 lacks symmetricality, so 'you can get there, but you can't get back', which makes the starting point special. So if you think the actual world has a special place in modal metaphysics, you must reject S5? |
18073 | Dummett says classical logic rests on meaning as truth, while intuitionist logic rests on assertability [Dummett, by Kitcher] |
Full Idea: Dummett argues that classical logic depends on the choice of the concept of truth as central to the theory of meaning, while for the intuitionist the concept of assertability occupies this position. | |
From: report of Michael Dummett (The philosophical basis of intuitionist logic [1973]) by Philip Kitcher - The Nature of Mathematical Knowledge 06.5 | |
A reaction: Since I can assert any nonsense I choose, this presumably means 'warranted' assertability, which is tied to the concept of proof in mathematics. You can reason about falsehoods, or about uninterpreted variables. Can you 'assert' 'Fx'? |
18832 | Mathematical statements and entities that result from an infinite process must lack a truth-value [Dummett] |
Full Idea: On an intuitionistic view, neither the truth-value of a statement nor any other mathematical entity can be given as the final result of an infinite process, since an infinite process is precisely one that does not have a final result. | |
From: Michael Dummett (Elements of Intuitionism (2nd ed) [2000], p.41), quoted by Ian Rumfitt - The Boundary Stones of Thought 7.3 | |
A reaction: This is rather a persuasive reason to sympathise with intuitionism. Mathematical tricks about 'limits' have lured us into believing in completed infinities, but actually that idea is incoherent. |
10537 | The ordered pairs <x,y> can be reduced to the class of sets of the form {{x},{x,y}} [Dummett] |
Full Idea: A classic reduction is the class of ordered pairs <x,y> being reduced to the class of sets of the form {{x},{x,y}}. | |
From: Michael Dummett (Frege Philosophy of Language (2nd ed) [1973], Ch.14) |
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. |
10542 | To associate a cardinal with each set, we need the Axiom of Choice to find a representative [Dummett] |
Full Idea: We may suppose that with each set is associated an object as its cardinal number, but we have no systematic way, without appeal to the Axiom of Choice, of selecting a representative set of each cardinality. | |
From: Michael Dummett (Frege Philosophy of Language (2nd ed) [1973], Ch.14) |