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Single Idea 18094

[filed under theme 6. Mathematics / A. Nature of Mathematics / 3. Nature of Numbers / i. Reals from cuts ]

Full Idea

One view, favoured by Dedekind, is that the cut postulates a real number for each cut in the rationals; it does not identify real numbers with cuts. ....A view favoured by later logicists is simply to identify a real number with a cut.

Gist of Idea

Dedekind says each cut matches a real; logicists say the cuts are the reals

Source

report of Richard Dedekind (Nature and Meaning of Numbers [1888]) by David Bostock - Philosophy of Mathematics 4.4

Book Ref

Bostock,David: 'Philosophy of Mathematics: An Introduction' [Wiley-Blackwell 2009], p.99


A Reaction

Dedekind is the patriarch of structuralism about mathematics, so he has little interest in the existenc of 'objects'.


The 11 ideas with the same theme [defining real numbers by cutting the line of rationals]:

A cut between rational numbers creates and defines an irrational number [Dedekind]
I say the irrational is not the cut itself, but a new creation which corresponds to the cut [Dedekind]
Dedekind's axiom that his Cut must be filled has the advantages of theft over honest toil [Dedekind, by Russell]
Dedekind says each cut matches a real; logicists say the cuts are the reals [Dedekind, by Bostock]
A series can be 'Cut' in two, where the lower class has no maximum, the upper no minimum [Russell]
A real number is the class of rationals less than the number [Russell/Whitehead, by Shapiro]
Points are 'continuous' if any 'cut' point participates in both halves of the cut [Harré/Madden]
For Eudoxus cuts in rationals are unique, but not every cut makes a real number [Bostock]
Why should a Dedekind cut correspond to a number? [Fine,K]
Cuts are made by the smallest upper or largest lower number, some of them not rational [Shapiro]
The two sides of the Cut are, roughly, the bounding commensurable ratios [Lavine]