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Single Idea 10250

[filed under theme 6. Mathematics / B. Foundations for Mathematics / 3. Axioms for Geometry ]

Full Idea

Euclid gives no principle of continuity, which would sanction an inference that if a line goes from the outside of a circle to the inside of circle, then it must intersect the circle at some point.

Gist of Idea

Euclid needs a principle of continuity, saying some lines must intersect

Source

comment on Euclid (Elements of Geometry [c.290 BCE]) by Stewart Shapiro - Philosophy of Mathematics 6.1 n2

Book Ref

Shapiro,Stewart: 'Philosophy of Mathematics:structure and ontology' [OUP 1997], p.183

A Reaction

Cantor and Dedekind began to contemplate discontinuous lines.

The 21 ideas with the same theme [formal starting points for deriving geometry]:

22278 Euclid relied on obvious properties in diagrams, as well as on his axioms [Potter on Euclid]
8673 Euclid's parallel postulate defines unique non-intersecting parallel lines [Euclid, by Friend]
10250 Euclid needs a principle of continuity, saying some lines must intersect [Shapiro on Euclid]
10302 Euclid says we can 'join' two points, but Hilbert says the straight line 'exists' [Euclid, by Bernays]
14157 Modern geometries only accept various parts of the Euclid propositions [Russell on Euclid]
13007 Archimedes defined a straight line as the shortest distance between two points [Archimedes, by Leibniz]
12937 We shouldn't just accept Euclid's axioms, but try to demonstrate them [Leibniz]
3343 Euclid's could be the only viable geometry, if rejection of the parallel line postulate doesn't lead to a contradiction [Benardete,JA on Kant]
17965 The whole of Euclidean geometry derives from a basic equation and transformations [Hilbert]
9546 Euclid axioms concerns possibilities of construction, but Hilbert's assert the existence of objects [Hilbert, by Chihara]
18742 Hilbert's formalisation revealed implicit congruence axioms in Euclid [Hilbert, by Horsten/Pettigrew]
18217 Hilbert's geometry is interesting because it captures Euclid without using real numbers [Hilbert, by Field,H]
10052 Geometry is united by the intuitive axioms of projective geometry [Russell, by Musgrave]
10157 Tarski improved Hilbert's geometry axioms, and without set-theory [Tarski, by Feferman/Feferman]
8997 There are four different possible conventional accounts of geometry [Quine]
18156 Modern axioms of geometry do not need the real numbers [Bostock]
18221 'Metric' axioms uses functions, points and numbers; 'synthetic' axioms give facts about space [Field,H]
13474 Euclid has a unique parallel, spherical geometry has none, and saddle geometry has several [Hart,WD]
9553 Analytic geometry gave space a mathematical structure, which could then have axioms [Chihara]
18760 The culmination of Euclidean geometry was axioms that made all models isomorphic [McGee]
17762 In non-Euclidean geometry, all Euclidean theorems are valid that avoid the fifth postulate [Walicki]