46 ideas
9542 | The best known axiomatization of PL is Whitehead/Russell, with four axioms and two rules [Russell/Whitehead, by Hughes/Cresswell] |
Full Idea: The best known axiomatization of PL is Whitehead/Russell. There are four axioms: (p∨p)→p, q→(p∨q), (p→q)→(q∨p), and (q→r)→((p∨q)→(p∨r)), plus Substitution and Modus Ponens rules. | |
From: report of B Russell/AN Whitehead (Principia Mathematica [1913]) by GE Hughes/M Cresswell - An Introduction to Modal Logic Ch.1 |
21720 | Russell saw Reducibility as legitimate for reducing classes to logic [Linsky,B on Russell/Whitehead] |
Full Idea: The axiom of Reducibility ...is crucial in the reduction of classes to logic, ...and seems to be a quite legitimate logical notion for Russell. | |
From: comment on B Russell/AN Whitehead (Principia Mathematica [1913]) by Bernard Linsky - Russell's Metaphysical Logic 6.4 | |
A reaction: This is an unusual defence of the axiom, which is usually presumed to have been kicked into the long grass by Quine. If one could reduce classes to logic, that would destroy the opposition to logicism in a single neat coup. |
10044 | Russell denies extensional sets, because the null can't be a collection, and the singleton is just its element [Russell/Whitehead, by Shapiro] |
Full Idea: Russell adduces two reasons against the extensional view of classes, namely the existence of the null class (which cannot very well be a collection), and the unit classes (which would have to be identical with their single elements). | |
From: report of B Russell/AN Whitehead (Principia Mathematica [1913]) by Stewart Shapiro - Structure and Ontology p.459 | |
A reaction: Gödel believes in the reality of classes. I have great sympathy with Russell, when people start to claim that sets are not just conveniences to help us think about things, but actual abstract entities. Is the singleton of my pencil is on this table? |
18208 | We regard classes as mere symbolic or linguistic conveniences [Russell/Whitehead] |
Full Idea: Classes, so far as we introduce them, are merely symbolic or linguistic conveniences, not genuine objects. | |
From: B Russell/AN Whitehead (Principia Mathematica [1913], p.72), quoted by Penelope Maddy - Naturalism in Mathematics III.2 |
8204 | Lewis's 'strict implication' preserved Russell's confusion of 'if...then' with implication [Quine on Russell/Whitehead] |
Full Idea: Russell call 'if...then' implication, when the material conditional is a much better account; C.I.Lewis (in founding modern modal logic) preserved Russell's confusion by creating 'strict implication', and called that implication. | |
From: comment on B Russell/AN Whitehead (Principia Mathematica [1913]) by Willard Quine - Reply to Professor Marcus p.177 | |
A reaction: [A compession of Quine's paragraph]. All of this assumes that logicians can give an accurate account of what if...then means, when ordinary usage is broad and vague. Strict implication seems to drain all the normal meaning out of 'if...then'. |
9359 | Russell's implication means that random sentences imply one another [Lewis,CI on Russell/Whitehead] |
Full Idea: In Mr Russell's idea of implication, if twenty random sentences from a newspaper were put in a hat, and two of them drawn at random, one will certainly imply the other, and it is an even bet the implication will be mutual. | |
From: comment on B Russell/AN Whitehead (Principia Mathematica [1913]) by C.I. Lewis - A Pragmatic Conception of the A Priori p.366 | |
A reaction: This sort of lament leads modern logicians to suggest 'relevance' as an important criterion. It certainly seems odd that so-called 'classical logic' should contain a principle so at variance with everyday reasoning. |
21707 | Russell unusually saw logic as 'interpreted' (though very general, and neutral) [Russell/Whitehead, by Linsky,B] |
Full Idea: Russell did not view logic as an uninterpreted calculus awaiting interpretations [the modern view]. Rather, logic is a single 'interpreted' body of a priori truths, of propositions rather than sentence forms - but maximally general and topic neutral. | |
From: report of B Russell/AN Whitehead (Principia Mathematica [1913]) by Bernard Linsky - Russell's Metaphysical Logic 1 | |
A reaction: This is the view which Wittgenstein challenged, saying logic is just conventional. Linsky claims that Russell's logicism is much more plausible, once you understand his view of logic. |
10036 | In 'Principia' a new abstract theory of relations appeared, and was applied [Russell/Whitehead, by Gödel] |
Full Idea: In 'Principia' a young science was enriched with a new abstract theory of relations, ..and not only Cantor's set theory but also ordinary arithmetic and the theory of measurement are treated from this abstract relational standpoint. | |
From: report of B Russell/AN Whitehead (Principia Mathematica [1913]) by Kurt Gödel - Russell's Mathematical Logic p.448 | |
A reaction: I presume this is accounting for relations in terms of ordered sets. |
18248 | A real number is the class of rationals less than the number [Russell/Whitehead, by Shapiro] |
Full Idea: For Russell the real number 2 is the class of rationals less than 2 (i.e. 2/1). ...Notice that on this definition, real numbers are classes of rational numbers. | |
From: report of B Russell/AN Whitehead (Principia Mathematica [1913]) by Stewart Shapiro - Thinking About Mathematics 5.2 |
18152 | Russell takes numbers to be classes, but then reduces the classes to numerical quantifiers [Russell/Whitehead, by Bostock] |
Full Idea: Although Russell takes numbers to be certain classes, his 'no-class' theory then eliminates all mention of classes in favour of the 'propositional functions' that define them; and in the case of the numbers these just are the numerical quantifiers. | |
From: report of B Russell/AN Whitehead (Principia Mathematica [1913]) by David Bostock - Philosophy of Mathematics 9.B.4 |
10025 | Russell and Whitehead took arithmetic to be higher-order logic [Russell/Whitehead, by Hodes] |
Full Idea: Russell and Whitehead took arithmetic to be higher-order logic, ..and came close to identifying numbers with numerical quantifiers. | |
From: report of B Russell/AN Whitehead (Principia Mathematica [1913]) by Harold Hodes - Logicism and Ontological Commits. of Arithmetic p.148 | |
A reaction: The point here is 'higher-order'. |
8683 | Russell and Whitehead were not realists, but embraced nearly all of maths in logic [Russell/Whitehead, by Friend] |
Full Idea: Unlike Frege, Russell and Whitehead were not realists about mathematical objects, and whereas Frege thought that only arithmetic and analysis are branches of logic, they think the vast majority of mathematics (including geometry) is essentially logical. | |
From: report of B Russell/AN Whitehead (Principia Mathematica [1913]) by Michčle Friend - Introducing the Philosophy of Mathematics 3.1 | |
A reaction: If, in essence, Descartes reduced geometry to algebra (by inventing co-ordinates), then geometry ought to be included. It is characteristic of Russell's hubris to want to embrace everything. |
10037 | 'Principia' lacks a precise statement of the syntax [Gödel on Russell/Whitehead] |
Full Idea: What is missing, above all, in 'Principia', is a precise statement of the syntax of the formalism. | |
From: comment on B Russell/AN Whitehead (Principia Mathematica [1913]) by Kurt Gödel - Russell's Mathematical Logic p.448 |
10093 | The ramified theory of types used propositional functions, and covered bound variables [Russell/Whitehead, by George/Velleman] |
Full Idea: Russell and Whitehead's ramified theory of types worked not with sets, but with propositional functions (similar to Frege's concepts), with a more restrictive assignment of variables, insisting that bound, as well as free, variables be of lower type. | |
From: report of B Russell/AN Whitehead (Principia Mathematica [1913]) by A.George / D.J.Velleman - Philosophies of Mathematics Ch.3 | |
A reaction: I don't fully understand this (and no one seems much interested any more), but I think variables are a key notion, and there is something interesting going on here. I am intrigued by ordinary language which behaves like variables. |
8691 | The Russell/Whitehead type theory was limited, and was not really logic [Friend on Russell/Whitehead] |
Full Idea: The Russell/Whitehead type theory reduces mathematics to a consistent founding discipline, but is criticised for not really being logic. They could not prove the existence of infinite sets, and introduced a non-logical 'axiom of reducibility'. | |
From: comment on B Russell/AN Whitehead (Principia Mathematica [1913]) by Michčle Friend - Introducing the Philosophy of Mathematics 3.6 | |
A reaction: To have reduced most of mathematics to a founding discipline sounds like quite an achievement, and its failure to be based in pure logic doesn't sound too bad. However, it seems to reduce some maths to just other maths. |
10305 | In 'Principia Mathematica', logic is exceeded in the axioms of infinity and reducibility, and in the domains [Bernays on Russell/Whitehead] |
Full Idea: In the system of 'Principia Mathematica', it is not only the axioms of infinity and reducibility which go beyond pure logic, but also the initial conception of a universal domain of individuals and of a domain of predicates. | |
From: comment on B Russell/AN Whitehead (Principia Mathematica [1913], p.267) by Paul Bernays - On Platonism in Mathematics p.267 | |
A reaction: This sort of criticism seems to be the real collapse of the logicist programme, rather than Russell's paradox, or Gödel's Incompleteness Theorems. It just became impossible to stick strictly to logic in the reduction of arithmetic. |
8684 | Russell and Whitehead consider the paradoxes to indicate that we create mathematical reality [Russell/Whitehead, by Friend] |
Full Idea: Russell and Whitehead are particularly careful to avoid paradox, and consider the paradoxes to indicate that we create mathematical reality. | |
From: report of B Russell/AN Whitehead (Principia Mathematica [1913]) by Michčle Friend - Introducing the Philosophy of Mathematics 3.1 | |
A reaction: This strikes me as quite a good argument. It is certainly counterintuitive that reality, and abstractions from reality, would contain contradictions. The realist view would be that we have paradoxes because we have misdescribed the facts. |
8746 | To avoid vicious circularity Russell produced ramified type theory, but Ramsey simplified it [Russell/Whitehead, by Shapiro] |
Full Idea: Russell insisted on the vicious circle principle, and thus rejected impredicative definitions, which resulted in an unwieldy ramified type theory, with the ad hoc axiom of reducibility. Ramsey's simpler theory was impredicative and avoided the axiom. | |
From: report of B Russell/AN Whitehead (Principia Mathematica [1913]) by Stewart Shapiro - Thinking About Mathematics 5.2 | |
A reaction: Nowadays the theory of types seems to have been given up, possibly because it has no real attraction if it lacks the strict character which Russell aspired to. |
22427 | To explain object qualities, primary qualities must be more than mere sources of experience [McGinn] |
Full Idea: In order that we have available an explanation of the qualities of objects we need to be able to conceive primary qualities as consisting in something other than powers to produce experiences. | |
From: Colin McGinn (Subjective View: sec qualities and indexicals [1983], 6 n 52) | |
A reaction: I suppose if the qualities are nothing more than the source of the experiences, that is Kant's noumenon. Nothing more could be said. The seems to be a requirement for tacit inference here. We infer the interior of the tomato. |
16661 | There are two sorts of category - referring to things, and to circumstances of things [Boethius] |
Full Idea: Is it not now clear what the difference is between items in the categories? Some serve to refer to a thing, whereas others serve to refer to the circumstances of a thing. | |
From: Boethius (Concerning the Trinity [c.518], Ch. 4), quoted by Robert Pasnau - Metaphysical Themes 1274-1671 12.5 |
12033 | An object is identical with itself, and no different indiscernible object can share that [Russell/Whitehead, by Adams,RM] |
Full Idea: Trivially, the Identity of Indiscernibles says that two individuals, Castor and Pollux, cannot have all properties in common. For Castor must have the properties of being identical with Castor and not being identical with Pollux, which Pollux can't share. | |
From: report of B Russell/AN Whitehead (Principia Mathematica [1913], I p.57) by Robert Merrihew Adams - Primitive Thisness and Primitive Identity 2 | |
A reaction: I suspect that either the property of being identical with itself is quite vacuous, or it is parasytic on primitive identity, or it is the criterion which is actually used to define identity. Either way, I don't find this claim very illuminating. |
22413 | Being red simply consists in looking red [McGinn] |
Full Idea: What we should claim is that being red consists in looking red. | |
From: Colin McGinn (Subjective View: sec qualities and indexicals [1983], 2) | |
A reaction: A very nice simple account. There is more to being square than looking square (which may not even guarantee that it is square). That's the primary/secondary distinction in a nut shell. But red things don't look red in the dark. Sufficient, not necessary. |
22415 | Relativity means differing secondary perceptions are not real disagreements [McGinn] |
Full Idea: Relativity permits differences in the perceived secondary qualities not to imply genuine disagreement, whereas perceived differences of primary qualities imply that at least one perceiver is in error. | |
From: Colin McGinn (Subjective View: sec qualities and indexicals [1983], 2) | |
A reaction: An example of 'relativity' is colour blindness. Sounds good, but what of one perceiver seeing a square as square, and another seeing it obliquely as a parallelogram? The squareness then seems more like a theory than a perception. |
22416 | Phenomenalism is correct for secondary qualities, so scepticism is there impossible [McGinn] |
Full Idea: We might say that scepticism is ruled out for secondary qualities because (roughly) phenomenalism is correct for them; but phenomenalism is not similarly correct for primary qualities, and scepticism cannot get a foothold. | |
From: Colin McGinn (Subjective View: sec qualities and indexicals [1983], 2) | |
A reaction: An odd idea, if phenomenalism says that reality consists entirely of phenomena. I should think phenomenalism is a commitment to the absence of primary qualities. |
22422 | Maybe all possible sense experience must involve both secondary and primary qualities [McGinn] |
Full Idea: The inseparability thesis about perception says that for any actual and possible sense the content of experiences delivered by that sense must be both of secondary qualities and of primary qualities. | |
From: Colin McGinn (Subjective View: sec qualities and indexicals [1983], 6) | |
A reaction: That would mean that all possible experience must have a mode of presentation, and also must be 'of' something independent of experience. So a yellow after-image would not count as an 'experience'? |
22428 | You understood being red if you know the experience involved; not so with thngs being square [McGinn] |
Full Idea: To grasp what it is to be red is to know the kind of sensory experience red things produce; ...but it is not true that to grasp what it is to be square one needs to know what kinds of sensory experience square things produce. | |
From: Colin McGinn (Subjective View: sec qualities and indexicals [1983], 8) | |
A reaction: Are any experiences involved in the understanding of squareness? We don't know squareness by a priori intuition (do we?). To grasp squareness if may be necessary to have a variety of experiences of it. Or to grasp that it is primary. |
22414 | You don't need to know how a square thing looks or feels to understand squareness [McGinn] |
Full Idea: To grasp what it is for something to be square it is not constitutively necessary to know how square things look or feel, since what it is to be square does not involve any such relation to experience. | |
From: Colin McGinn (Subjective View: sec qualities and indexicals [1983], 2) | |
A reaction: You could even describe squareness verbally, unlike redness. It seems crucial that almost any sense (such as bat echoes) can communicate primary qualities, but secondary qualities are tied to a sense, and wouldn't exist without it. |
22423 | Touch doesn't provide direct experience of primary qualities, because touch feels temperature [McGinn] |
Full Idea: Bennett's claim that touch provides experience of primary qualities without experience of any secondary qualities strikes me as false, because tactile experience includes felt temperature, which is a dispositional secondary quality. | |
From: Colin McGinn (Subjective View: sec qualities and indexicals [1983], 6) | |
A reaction: [J.Bennett 1971 pp. 90-4] Fair point. What about shape and texture? We experience forces, but the shape is assembled in imagination rather than in experience. So do we meet primary qualities directly in forces, such as acceleration? No secondary quality? |
22426 | We can perceive objectively, because primary qualities are not mind-created [McGinn] |
Full Idea: I hold that experience succeeds in representing the world objectively, since primary quality perceptual content is not contributed by the mind. | |
From: Colin McGinn (Subjective View: sec qualities and indexicals [1983], 6) | |
A reaction: My new example of a direct perception of a primary quality is acceleration in a lift. What would we say to one passenger who denied feeling the acceleration? It took an effort to see that mind contributes to secondary qualities (so make more effort?). |
22412 | Lockean secondary qualities (unlike primaries) produce particular sensory experiences [McGinn] |
Full Idea: In the Lockean tradition, secondary qualities are defined as those whose instantiation in an object consists in a power or disposition of the object to produce sensory experiences in perceivers of a certain phenomenological character. | |
From: Colin McGinn (Subjective View: sec qualities and indexicals [1983], 2) | |
A reaction: Primary qualities are said to lack such dispositions. Not sure about these definitions. Primaries offer no experiences? With these definitions, comparing them would be a category mistake. I take it primaries reflect reality and secondaries do not. |
22421 | Could there be a mind which lacked secondary quality perception? [McGinn] |
Full Idea: Can we form a conception of a type of mind whose representations are free of secondary quality perceptions? | |
From: Colin McGinn (Subjective View: sec qualities and indexicals [1983], 6) | |
A reaction: Nice question. Minds must have experiences, and there has to be a 'way' or 'mode' for those experiences. A mind which directly grasped the primary quality of sphericity would seem to be visionary rather than sensual or experiential. |
22424 | Secondary qualities contain information; their variety would be superfluous otherwise [McGinn] |
Full Idea: Surely we learn something about an object when we discover its secondary qualities? ...If secondary quality experience were informationally inert, its variety would be something of a puzzle. Why not employ the same medium for all primary informaton? | |
From: Colin McGinn (Subjective View: sec qualities and indexicals [1983], 6) | |
A reaction: This is important. We can't just focus on the primary qualities, and ignore the secondary. But diverse colours draw attention to information, which can then be translated into neutral data, as in spectroscopic analysis. Locke agrees with this. |
22425 | The utility theory says secondary qualities give information useful to human beings [McGinn] |
Full Idea: Secondary quality perception, according to the utility theory, gives information about the relation between the perceptual object and the perceiver's needs and interests. | |
From: Colin McGinn (Subjective View: sec qualities and indexicals [1983], 6) | |
A reaction: Almost the only example I can think of is whether fruit is ripe or rotten. ...Also 'bad' smells. We recognise aggressive animal noises, but that is not the same as dangerous (e.g. rustling snake). Divine design is behind this theory, I think. |
7629 | We see objects 'directly' by representing them [McGinn] |
Full Idea: My view is that we see objects 'directly' by representing them in visual experience. | |
From: Colin McGinn (Subjective View: sec qualities and indexicals [1983], Ch.8 n1) | |
A reaction: [Quoted by Maund] This rejects both inference in perception and sense-data, while retaining the notion of representation. It is a view which has gained a lot of support. But how can it be direct if it represents? Photographs can't do that. |
10040 | Russell showed, through the paradoxes, that our basic logical intuitions are self-contradictory [Russell/Whitehead, by Gödel] |
Full Idea: By analyzing the paradoxes to which Cantor's set theory had led, ..Russell brought to light the amazing fact that our logical intuitions (concerning such notions as truth, concept, being, class) are self-contradictory. | |
From: report of B Russell/AN Whitehead (Principia Mathematica [1913]) by Kurt Gödel - Russell's Mathematical Logic p.452 | |
A reaction: The main intuition that failed was, I take it, that every concept has an extension, that is, there are always objects which will or could fall under the concept. |
21725 | The multiple relations theory says assertions about propositions are about their ingredients [Russell/Whitehead, by Linsky,B] |
Full Idea: The multiple relations theory of judgement proposes that assertions about propositions are dependent upon genuine facts involving belief and other attitude relations, subjects of those attitudes, and the constituents of the belief. | |
From: report of B Russell/AN Whitehead (Principia Mathematica [1913]) by Bernard Linsky - Russell's Metaphysical Logic 7.2 | |
A reaction: This seems to require a commitment to universals (especially relations) with which we can be directly acquainted. I prefer propositions, but as mental entities, not platonic entities. |
23474 | A judgement is a complex entity, of mind and various objects [Russell/Whitehead] |
Full Idea: When a judgement occurs, there is a certain complex entity, composed of the mind and the various objects of the judgement. | |
From: B Russell/AN Whitehead (Principia Mathematica [1913], p.44) | |
A reaction: This is Russell's multiple-relation theory of judgement, which replaced his earlier belief in unified propositions (now 'false abstractions'). He seems to have accepted Locke's view, that the act of judgement produces the unity. |
23455 | The meaning of 'Socrates is human' is completed by a judgement [Russell/Whitehead] |
Full Idea: When I judge 'Socrates is human', the meaning is completed by the act of judging. | |
From: B Russell/AN Whitehead (Principia Mathematica [1913], p.44), quoted by Michael Morris - Guidebook to Wittgenstein's Tractatus | |
A reaction: Morris says this is Russell's multiple-relations theory of judgement. The theory accompanies the rejection of the concept of the unified proposition. When I hear 'Socrates had a mole on his shoulder' I get the meaning without judging. |
23480 | The multiple relation theory of judgement couldn't explain the unity of sentences [Morris,M on Russell/Whitehead] |
Full Idea: When Russell moved to his multiple relation theory of judgement …he then faced difficulties making sense of the unity of sentences. | |
From: comment on B Russell/AN Whitehead (Principia Mathematica [1913], p.44) by Michael Morris - Guidebook to Wittgenstein's Tractatus 3A | |
A reaction: Roughly, he seems committed to saying that there is only unity if you think there is unity; there is no unity in a sentence prior to the act of judgement. |
18275 | Only the act of judging completes the meaning of a statement [Russell/Whitehead] |
Full Idea: When I judge 'Socrates is human', the meaning is completed by the act of judging, and we no longer have an incomplete symbol. | |
From: B Russell/AN Whitehead (Principia Mathematica [1913], p.44), quoted by J. Alberto Coffa - The Semantic Tradition from Kant to Carnap | |
A reaction: Personally I would have thought that you needed to know the meaning properly before you could make the judgement, but then he is Bertrand Russell and I'm not. |
22420 | The indexical perspective is subjective, incorrigible and constant [McGinn] |
Full Idea: I attribute three properties to the indexical perspective: it is subjective, incorrigible, and constant. | |
From: Colin McGinn (Subjective View: sec qualities and indexicals [1983], 5) | |
A reaction: That is as good an idea as any for summarising the view (associated with John Perry) that the indexical perspective is an indispensable feature of reality. For a good attack on this, which I favour, see Cappelen and Dever. |
18410 | Indexical thought is in relation to my self-consciousness [McGinn] |
Full Idea: Very roughly, we can say that to think of something indexically is to think of it in relation to me, as I am presented to myself in self-consciousness. | |
From: Colin McGinn (Subjective View: sec qualities and indexicals [1983], 2) | |
A reaction: So it is characterised relationally, which doesn't mean it has a distinctive intrinsic character. If I'm lost, and I overhear someone say 'Peter is in Hazlemere', I get the same relational information (in a different mode) without the indexicality. |
22417 | Indexicals do not figure in theories of physics, because they are not explanatory causes [McGinn] |
Full Idea: Indexicals are like secondary qualities in not figuring in causal explanations of the interactions of objects: physics omits them not because they are relative and egocentric, but because they do not constitute explanatory predicates of a causal theory. | |
From: Colin McGinn (Subjective View: sec qualities and indexicals [1983], 2) | |
A reaction: They are outside explanatory physics, but not outside explanation. The object moved because a force acted on it; or the object moved because I wanted it moved. |
18402 | Indexical concepts are indispensable, as we need them for the power to act [McGinn] |
Full Idea: The present suggestion is that indexical concepts are ineliminable because without them agency would be impossible: when I imagine myself divested of indexical thoughts employing only centreless mental representations, I am deprived of the power to act. | |
From: Colin McGinn (Subjective View: sec qualities and indexicals [1983], 6) | |
A reaction: A nice clear statement of the view developed by Perry and Lewis. I agree with Cappelen and Dever that it is entirely wrong, and that indexical thought is entirely eliminable, and nothing special. |
22418 | I can know indexical truths a priori, unlike their non-indexical paraphrases [McGinn] |
Full Idea: I know the truth of the sentence 'I am here now' a priori, but I do not know a priori 'McGinn is in London on 15th Nov 1981'. | |
From: Colin McGinn (Subjective View: sec qualities and indexicals [1983], 3) | |
A reaction: I'm not convinced that I can grasp the concepts of 'here' and 'now' (i.e. space and time) by purely a priori means. But he certainly shows that you can't glibly dismiss indexicals by paraphrasing them in that way. |
23453 | Propositions as objects of judgement don't exist, because we judge several objects, not one [Russell/Whitehead] |
Full Idea: A 'proposition', in the sense in which a proposition is supposed to be the object of a judgement, is a false abstraction, because a judgement has several objects, not one. | |
From: B Russell/AN Whitehead (Principia Mathematica [1913], p.44), quoted by Michael Morris - Guidebook to Wittgenstein's Tractatus 2E | |
A reaction: This is the rejection of the 'Russellian' theory of propositions, in favour of his multiple-relations theory of judgement. But why don't the related objects add up to a proposition about a state of affairs? |