19 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 |
| 16052 | 'Superdupervenience' is supervenience that has a robustly materialistic explanation [Horgan,T] |
| Full Idea: The idea of a ontological supervenience that is robustly explainable in a materialistically explainable way I hereby dub 'superdupervenience'. | |
| From: Terence Horgan (From Supervenience to Superdupervenience [1993], §4) | |
| A reaction: [He credits William Lycan with the actual word] His assumption prior to this introduction is that mere supervenience just adds a new mystery. I take supervenience to be an observation of 'tracking', which presumably needs to be explained. |
| 16053 | 'Global' supervenience is facts tracking varying physical facts in every possible world [Horgan,T] |
| Full Idea: The idea of 'global supervenience' is standardly expressed as 'there are no two physically possible worlds which are exactly alike in all physical respects but different in some other respect'. | |
| From: Terence Horgan (From Supervenience to Superdupervenience [1993], §5) | |
| A reaction: [Jaegwon Kim is the source of this concept] The 'local' view will be that they do indeed track, but they could, in principle, come apart. A zombie might be a case of them possibly coming apart. Zombies are silly. |
| 16056 | Don't just observe supervenience - explain it! [Horgan,T] |
| Full Idea: Although the task of explaining supervenience has been little appreciated and little discussed in the philosophical literature, it is time for that to change. | |
| From: Terence Horgan (From Supervenience to Superdupervenience [1993], §8) | |
| A reaction: I would offer a strong addition to this: be absolutely sure that you are dealing with two distinct things in the supervenience relationship, before you waste time trying to explain how they relate to one another. |
| 16054 | Physicalism needs more than global supervenience on the physical [Horgan,T] |
| Full Idea: Global supervenience seems too weak to capture the physical facts determining all the facts. …There could be two spatio-temporal regions alike in all physical respects, but different in some intrinsic non-physical respect. | |
| From: Terence Horgan (From Supervenience to Superdupervenience [1993], §5) | |
| A reaction: I.e. there might be two physically identical regions, but one contains angels and the other doesn't (so the extra fact isn't tracking the physical facts). Physicalism I take to be the simple denial of the angels. Supervenience is an explanandum. |
| 16055 | Materialism requires that physics be causally complete [Horgan,T] |
| Full Idea: Any broadly materialistic metaphysical position needs to claim that physics is causally complete. | |
| From: Terence Horgan (From Supervenience to Superdupervenience [1993], §6) | |
| A reaction: Since 'physics' is a human creation, I presume he means that physical reality is causally complete. The interaction problem that faced Descartes seems crucial - how could something utterly non-physical effect a physical change? |
| 16057 | Instrumentalism normally says some discourse is useful, but not genuinely true [Horgan,T] |
| Full Idea: Instrumentalist views typically attribute utility to the given body of discourse, but deny that it expresses genuine truths. | |
| From: Terence Horgan (From Supervenience to Superdupervenience [1993], §8) | |
| A reaction: To me it is obvious to ask why anything could have a high level of utility (especially in accounts of the external physical world) without being true. Falsehoods may sometimes (though I doubt it) be handy in human life, but useful in chemistry…? |
| 18665 | Moral problems are responsibility conflicts, needing contextual and narrative attention to relationships [Gilligan] |
| Full Idea: The moral problem arises from conflicting responsibilities rather than competing rights, and its resolution needs contextual and narrative thinking. This morality as care centers around the understanding of responsibility and relationships. | |
| From: Carol Gilligan (In a Different Voice [1982], p.19), quoted by Will Kymlicka - Contemporary Political Philosophy (1st edn) | |
| A reaction: [Kymlicka cites her as a key voice in feminist moral philosophy] I like all of this, especially the very original thought (to me, anyway) that moral thinking should be 'narrative' in character. |