Combining Texts

All the ideas for 'fragments/reports', 'Letters to Russell' and 'The Philosophy of Mathematics'

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12 ideas

4. Formal Logic / F. Set Theory ST / 4. Axioms for Sets / a. Axioms for sets

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.

5. Theory of Logic / D. Assumptions for Logic / 2. Excluded Middle

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.

5. Theory of Logic / G. Quantification / 5. Second-Order Quantification

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.

5. Theory of Logic / I. Semantics of Logic / 3. Logical Truth

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?

6. Mathematics / A. Nature of Mathematics / 3. Nature of Numbers / c. Priority of numbers

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.

6. Mathematics / A. Nature of Mathematics / 3. Nature of Numbers / g. Real numbers

18253	I wish to go straight from cardinals to reals (as ratios), leaving out the rationals [Frege]
	Full Idea: You need a double transition, from cardinal numbes (Anzahlen) to the rational numbers, and from the latter to the real numbers generally. I wish to go straight from the cardinal numbers to the real numbers as ratios of quantities.
	From: Gottlob Frege (Letters to Russell [1902], 1903.05.21), quoted by Michael Dummett - Frege philosophy of mathematics 21 'Frege's'
	A reaction: Note that Frege's real numbers are not quantities, but ratios of quantities. In this way the same real number can refer to lengths, masses, intensities etc.

6. Mathematics / B. Foundations for Mathematics / 7. Mathematical Structuralism / e. Structuralism critique

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.

6. Mathematics / C. Sources of Mathematics / 6. Logicism / a. Early logicism

18166	The loss of my Rule V seems to make foundations for arithmetic impossible [Frege]
	Full Idea: With the loss of my Rule V, not only the foundations of arithmetic, but also the sole possible foundations of arithmetic, seem to vanish.
	From: Gottlob Frege (Letters to Russell [1902], 1902.06.22)
	A reaction: Obviously he was stressed, but did he really mean that there could be no foundation for arithmetic, suggesting that the subject might vanish into thin air?

9. Objects / A. Existence of Objects / 2. Abstract Objects / c. Modern abstracta

18269	Logical objects are extensions of concepts, or ranges of values of functions [Frege]
	Full Idea: How are we to conceive of logical objects? My only answer is, we conceive of them as extensions of concepts or, more generally, as ranges of values of functions ...what other way is there?
	From: Gottlob Frege (Letters to Russell [1902], 1902.07.28), quoted by J. Alberto Coffa - The Semantic Tradition from Kant to Carnap 7 epigr
	A reaction: This is the clearest statement I have found of what Frege means by an 'object'. But an extension is a collection of things, so an object is a group treated as a unity, which is generally how we understand a 'set'. Hence Quine's ontology.

26. Natural Theory / A. Speculations on Nature / 5. Infinite in Nature

1748	Archelaus was the first person to say that the universe is boundless [Archelaus, by Diog. Laertius]
	Full Idea: Archelaus was the first person to say that the universe is boundless.
	From: report of Archelaus (fragments/reports [c.450 BCE]) by Diogenes Laertius - Lives of Eminent Philosophers 02.Ar.3

27. Natural Reality / G. Biology / 3. Evolution

5989	Archelaus said life began in a primeval slime [Archelaus, by Schofield]
	Full Idea: Archelaus wrote that life on Earth began in a primeval slime.
	From: report of Archelaus (fragments/reports [c.450 BCE]) by Malcolm Schofield - Archelaus
	A reaction: This sounds like a fairly clearcut assertion of the production of life by evolution. Darwin's contribution was to propose the mechanism for achieving it. We should honour the name of Archelaus for this idea.