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Ideas for 'Letters to Bentley', 'The Question of Ontology' and 'Lewis on Perdurance versus Endurance'

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5 ideas

6. Mathematics / A. Nature of Mathematics / 3. Nature of Numbers / a. Numbers
13152 We can talk of 'innumerable number', about the infinite points on a line [Newton]
     Full Idea: If any man shall take the words number and sum in a larger sense, to understand things which are numberless and sumless (such as the infinite points on a line), I could allow him the contradictious phrase 'innumerable number' without absurdity.
     From: Isaac Newton (Letters to Bentley [1692], 1693.02.25)
     A reaction: [compressed] I take the key point here to be the phrase of taking number 'in a larger sense'. Like the word 'atom' in physics, the word 'number' retains its traditional reference, but has considerably shifted its scope. Amateurs must live with this.
6. Mathematics / A. Nature of Mathematics / 5. The Infinite / a. The Infinite
13151 Not all infinites are equal [Newton]
     Full Idea: It is an error that all infinites are equal.
     From: Isaac Newton (Letters to Bentley [1692], 1693.01.17)
     A reaction: There follows a discussion of the mathematicians' view of infinity. Cantor was not the first to notice that there is more than one sort of of infinity.
6. Mathematics / B. Foundations for Mathematics / 5. Definitions of Number / c. Fregean numbers
12215 The existence of numbers is not a matter of identities, but of constituents of the world [Fine,K]
     Full Idea: On saying that a particular number exists, we are not saying that there is something identical to it, but saying something about its status as a genuine constituent of the world.
     From: Kit Fine (The Question of Ontology [2009], p.168)
     A reaction: This is aimed at Frege's criterion of identity, which is to be an element in an identity relation, such as x = y. Fine suggests that this only gives a 'trivial' notion of existence, when he is interested in a 'thick' sense of 'exists'.
6. Mathematics / C. Sources of Mathematics / 1. Mathematical Platonism / b. Against mathematical platonism
12211 It is plausible that x^2 = -1 had no solutions before complex numbers were 'introduced' [Fine,K]
     Full Idea: It is not implausible that before the 'introduction' of complex numbers, it would have been incorrect for mathematicians to claim that there was a solution to the equation 'x^2 = -1' under a completely unrestricted understanding of 'there are'.
     From: Kit Fine (The Question of Ontology [2009])
     A reaction: I have adopted this as the crucial test question for anyone's attitude to platonism in mathematics. I take it as obvious that complex numbers were simply invented so that such equations could be dealt with. They weren't 'discovered'!
6. Mathematics / C. Sources of Mathematics / 4. Mathematical Empiricism / a. Mathematical empiricism
12209 The indispensability argument shows that nature is non-numerical, not the denial of numbers [Fine,K]
     Full Idea: Arguments such as the dispensability argument are attempting to show something about the essentially non-numerical character of physical reality, rather than something about the nature or non-existence of the numbers themselves.
     From: Kit Fine (The Question of Ontology [2009], p.160)
     A reaction: This is aimed at Hartry Field. If Quine was right, and we only believe in numbers because of our science, and then Field shows our science doesn't need it, then Fine would be wrong. Quine must be wrong, as well as Field.