22 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. |
| 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 |
| 5303 | For the proletariate, law, morality and religion are just expressions of bourgeois interests [Marx/Engels] |
| Full Idea: Law, morality, religion are to the proletarian so many bourgeois prejudices, behind which lurk in ambush just as many bourgeois interests. | |
| From: K Marx / F Engels (The Communist Manifesto [1848], §1) | |
| A reaction: This Marxist idea has been the main driving force in spreading relativist views through modern culture. There is a lot of truth here, but philosophy is plausibly the search for truths which both the bourgeois and the proletarian will accept. |
| 21998 | Bourgeois interests create our morality, law and religion [Marx/Engels] |
| Full Idea: Morality, law and religion are bourgeois prejudices, behind which lurk in ambush just as many bourgeois interests. | |
| From: K Marx / F Engels (The Communist Manifesto [1848], p.230), quoted by Peter Singer - Marx 9 | |
| A reaction: The obvious question is whether this creation of values is conscious or unconscious. Personally I believe in conspiracies. Some cynical conversations go on behind the scenes, of which historians will never hear. |
| 5302 | Modern governments are just bourgeois management committees [Marx/Engels] |
| Full Idea: The executive of the modern State is but a committee for managing the common affairs of the whole bourgeoisie. | |
| From: K Marx / F Engels (The Communist Manifesto [1848], §1) | |
| A reaction: In Britain the Labour Party and the Trade Unions have appeared since 1848, but bourgeoisie control of the media has pushed us a long way back towards Marx's time. Government will always be someone's management committee. |
| 5304 | Communism aims to abolish not all property, but bourgeois property [Marx/Engels] |
| Full Idea: The distinguishing feature of Communism is not the abolition of property generally, but the abolition of bourgeois property. | |
| From: K Marx / F Engels (The Communist Manifesto [1848], §2) | |
| A reaction: This is a sinister remark which has led to huge numbers of murders in the Soviet Union and China. People resent having their property 'abolished', especially if they have worked hard for it. But most of our wealth is owned by about 2% of our people. |
| 5307 | Many of the bourgeois rights grievances are a form of self-defence [Marx/Engels] |
| Full Idea: A part of the bourgeoisie is desirous of redressing social grievances, in order to secure the continued existence of bourgeois society. | |
| From: K Marx / F Engels (The Communist Manifesto [1848], §3.II) | |
| A reaction: …so don't try being nice to us. No TRUE bourgeois would actually want to help the proletariate… Nevertheless, he is probably largely right. Do we want the poor to suffer? No. Do we want them to be as rich as us? No! |
| 5306 | The free development of each should be the condition for the free development of all [Marx/Engels] |
| Full Idea: In a communist society we shall have an association, in which the free development of each is the condition for the free development of all. | |
| From: K Marx / F Engels (The Communist Manifesto [1848], §2) | |
| A reaction: This ringing slogan is remarkably close to John Stuart Mill's defence of liberalism, where liberty is an absolute, as long as it avoids the liberty of others. Personally I think freedom is marginal in political philosophy, like food and shelter. |
| 5305 | Communists want to rescue education from the ruling class [Marx/Engels] |
| Full Idea: Communists seek to rescue education from the influence of the ruling class. | |
| From: K Marx / F Engels (The Communist Manifesto [1848], §2) | |
| A reaction: Someone has to control education, and I would personally prefer it if the controllers were well educated themselves. Neutral education is an idle dream. We must educate for democracy, if we really want democracy. |
| 5301 | The history of all existing society is the history of class struggles [Marx/Engels] |
| Full Idea: The history of all existing society is the history of class struggles. | |
| From: K Marx / F Engels (The Communist Manifesto [1848], §1) | |
| A reaction: This seems to make, say, the English Peasants' Revolt of 1481 crucial, and the building of Lincoln Cathedral fairly minor. Where does the advent of the telephone figure? Etc. Still, we must concede his point. Most medieval history is about power. |
| 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 |
| 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. |