18 ideas
8623 | Proof reveals the interdependence of truths, as well as showing their certainty [Euclid, by Frege] |
Full Idea: Euclid gives proofs of many things which anyone would concede to him without question. ...The aim of proof is not merely to place the truth of a proposition beyond doubt, but also to afford us insight into the dependence of truths upon one another. | |
From: report of Euclid (Elements of Geometry [c.290 BCE]) by Gottlob Frege - Grundlagen der Arithmetik (Foundations) §02 | |
A reaction: This connects nicely with Shoemaker's view of analysis (Idea 8559), which I will adopt as my general view. I've always thought of philosophy as the aspiration to wisdom through the cartography of concepts. |
13907 | If you pick an arbitrary triangle, things proved of it are true of all triangles [Euclid, by Lemmon] |
Full Idea: Euclid begins proofs about all triangles with 'let ABC be a triangle', but ABC is not a proper name. It names an arbitrarily selected triangle, and if that has a property, then we can conclude that all triangles have the property. | |
From: report of Euclid (Elements of Geometry [c.290 BCE]) by E.J. Lemmon - Beginning Logic 3.2 | |
A reaction: Lemmon adds the proviso that there must be no hidden assumptions about the triangle we have selected. You must generalise the properties too. Pick a triangle, any triangle, say one with three angles of 60 degrees; now generalise from it. |
20100 | Classical liberalism seeks freedom of opinion, of private life, of expression, and of property [Micklethwait/Wooldridge] |
Full Idea: The classical liberals agreed on a basic list of freedoms: of opinion (including religion), of private life, of expression, and of property | |
From: Micklethwait,J/Wooldridge,A (The Fourth Revolution [2014], 9) | |
A reaction: Mill is main articulator of this. Modern neo-liberals focus on economic freedom. Neither of them seem to make freedom of opportunity central, though I suspect our modern Liberal Party would. |
6297 | Euclid's geometry is synthetic, but Descartes produced an analytic version of it [Euclid, by Resnik] |
Full Idea: Euclid's geometry is a synthetic geometry; Descartes supplied an analytic version of Euclid's geometry, and we now have analytic versions of the early non-Euclidean geometries. | |
From: report of Euclid (Elements of Geometry [c.290 BCE]) by Michael D. Resnik - Maths as a Science of Patterns One.4 | |
A reaction: I take it that the original Euclidean axioms were observations about the nature of space, but Descartes turned them into a set of pure interlocking definitions which could still function if space ceased to exist. |
9603 | An assumption that there is a largest prime leads to a contradiction [Euclid, by Brown,JR] |
Full Idea: Assume a largest prime, then multiply the primes together and add one. The new number isn't prime, because we assumed a largest prime; but it can't be divided by a prime, because the remainder is one. So only a larger prime could divide it. Contradiction. | |
From: report of Euclid (Elements of Geometry [c.290 BCE]) by James Robert Brown - Philosophy of Mathematics Ch.1 | |
A reaction: Not only a very elegant mathematical argument, but a model for how much modern logic proceeds, by assuming that the proposition is false, and then deducing a contradiction from it. |
9894 | A unit is that according to which each existing thing is said to be one [Euclid] |
Full Idea: A unit is that according to which each existing thing is said to be one. | |
From: Euclid (Elements of Geometry [c.290 BCE], 7 Def 1) | |
A reaction: See Frege's 'Grundlagen' §29-44 for a sustained critique of this. Frege is good, but there must be something right about the Euclid idea. If I count stone, paper and scissors as three, each must first qualify to be counted as one. Psychology creeps in. |
8738 | Postulate 2 says a line can be extended continuously [Euclid, by Shapiro] |
Full Idea: Euclid's Postulate 2 says the geometer can 'produce a finite straight line continuously in a straight line'. | |
From: report of Euclid (Elements of Geometry [c.290 BCE]) by Stewart Shapiro - Thinking About Mathematics 4.2 | |
A reaction: The point being that this takes infinity for granted, especially if you start counting how many points there are on the line. The Einstein idea that it might eventually come round and hit you on the back of the head would have charmed Euclid. |
22278 | Euclid relied on obvious properties in diagrams, as well as on his axioms [Potter on Euclid] |
Full Idea: Euclid's axioms were insufficient to derive all the theorems of geometry: at various points in his proofs he appealed to properties that are obvious from the diagrams but do not follow from the stated axioms. | |
From: comment on Euclid (Elements of Geometry [c.290 BCE]) by Michael Potter - The Rise of Analytic Philosophy 1879-1930 03 'aim' | |
A reaction: I suppose if the axioms of a system are based on self-evidence, this would licence an appeal to self-evidence elsewhere in the system. Only pedants insist on writing down what is obvious to everyone! |
8673 | Euclid's parallel postulate defines unique non-intersecting parallel lines [Euclid, by Friend] |
Full Idea: Euclid's fifth 'parallel' postulate says if there is an infinite straight line and a point, then there is only one straight line through the point which won't intersect the first line. This axiom is independent of Euclid's first four (agreed) axioms. | |
From: report of Euclid (Elements of Geometry [c.290 BCE]) by Michèle Friend - Introducing the Philosophy of Mathematics 2.2 | |
A reaction: This postulate was challenged in the nineteenth century, which was a major landmark in the development of modern relativist views of knowledge. |
10250 | Euclid needs a principle of continuity, saying some lines must intersect [Shapiro on Euclid] |
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. | |
From: comment on Euclid (Elements of Geometry [c.290 BCE]) by Stewart Shapiro - Philosophy of Mathematics 6.1 n2 | |
A reaction: Cantor and Dedekind began to contemplate discontinuous lines. |
10302 | Euclid says we can 'join' two points, but Hilbert says the straight line 'exists' [Euclid, by Bernays] |
Full Idea: Euclid postulates: One can join two points by a straight line; Hilbert states the axiom: Given any two points, there exists a straight line on which both are situated. | |
From: report of Euclid (Elements of Geometry [c.290 BCE]) by Paul Bernays - On Platonism in Mathematics p.259 |
14157 | Modern geometries only accept various parts of the Euclid propositions [Russell on Euclid] |
Full Idea: In descriptive geometry the first 26 propositions of Euclid hold. In projective geometry the 1st, 7th, 16th and 17th require modification (as a straight line is not a closed series). Those after 26 depend on the postulate of parallels, so aren't assumed. | |
From: comment on Euclid (Elements of Geometry [c.290 BCE]) by Bertrand Russell - The Principles of Mathematics §388 |
1600 | Euclid's common notions or axioms are what we must have if we are to learn anything at all [Euclid, by Roochnik] |
Full Idea: The best known example of Euclid's 'common notions' is "If equals are subtracted from equals the remainders are equal". These can be called axioms, and are what "the man who is to learn anything whatever must have". | |
From: report of Euclid (Elements of Geometry [c.290 BCE], 72a17) by David Roochnik - The Tragedy of Reason p.149 |
1556 | By nature people are close to one another, but culture drives them apart [Hippias] |
Full Idea: I regard you all as relatives - by nature, not by convention. By nature like is akin to like, but convention is a tyrant over humankind and often constrains people to act contrary to nature. | |
From: Hippias (fragments/reports [c.430 BCE]), quoted by Plato - Protagoras 337c8 |
20097 | The welfare state aims at freedom from want, and equality of opportunity [Micklethwait/Wooldridge] |
Full Idea: In the classical liberal tradition freedom meant freedom from external control, and equality meant equality before the law. In the welfare state (of Beatrice Webb) freedom was reinterpreted as freedom from want, and equality as equality of opportunity. | |
From: Micklethwait,J/Wooldridge,A (The Fourth Revolution [2014], 3) | |
A reaction: The authors call this the 'third revolution' in government, after 17th century centralisation and early 19th century accountability. Tawney 1931 is the key text. |
20099 | For communists history is driven by the proletariat [Micklethwait/Wooldridge] |
Full Idea: For the communists the proletariat rather than the state was the locomotive of history. | |
From: Micklethwait,J/Wooldridge,A (The Fourth Revolution [2014], 3) | |
A reaction: I feel increasingly reluctant to support any party which appears to mainly represent the interests of a single social class, no matter how large that class may be. An attraction of liberalism is that it makes no reference to class. |
20098 | Fans of economic freedom claim that capitalism is self-correcting [Micklethwait/Wooldridge] |
Full Idea: The central laissez-faire conceit is that capitalism is a self-correcting mechanism. | |
From: Micklethwait,J/Wooldridge,A (The Fourth Revolution [2014], 3) | |
A reaction: This was Keynes's rather left-wing criticism of standard capitalist views. These resurfaced in the 1980s with mantras about the virtues of 'market forces'. |
20096 | Roman law entrenched property rights [Micklethwait/Wooldridge] |
Full Idea: Roman law entrenched property rights. | |
From: Micklethwait,J/Wooldridge,A (The Fourth Revolution [2014], 1 Intro) | |
A reaction: Normally attributed to Locke, so this is a good corrective. Was the principle gradually forgotten before Locke? |