10 ideas
| 17610 | The Axiom of Choice paradoxically allows decomposing a sphere into two identical spheres [Maddy] |
| Full Idea: One feature of the Axiom of Choice that troubled many mathematicians was the so-called Banach-Tarski paradox: using the Axiom, a sphere can be decomposed into finitely many parts and those parts reassembled into two spheres the same size as the original. | |
| From: Penelope Maddy (Defending the Axioms [2011], 1.3) | |
| A reaction: (The key is that the parts are non-measurable). To an outsider it is puzzling that the Axiom has been universally accepted, even though it produces such a result. Someone can explain that, I'm sure. |
| 17620 | Critics of if-thenism say that not all starting points, even consistent ones, are worth studying [Maddy] |
| Full Idea: If-thenism denies that mathematics is in the business of discovering truths about abstracta. ...[their opponents] obviously don't regard any starting point, even a consistent one, as equally worthy of investigation. | |
| From: Penelope Maddy (Defending the Axioms [2011], 3.3) | |
| A reaction: I have some sympathy with if-thenism, in that you can obviously study the implications of any 'if' you like, but deep down I agree with the critics. |
| 17605 | Hilbert's geometry and Dedekind's real numbers were role models for axiomatization [Maddy] |
| Full Idea: At the end of the nineteenth century there was a renewed emphasis on rigor, the central tool of which was axiomatization, along the lines of Hilbert's axioms for geometry and Dedekind's axioms for real numbers. | |
| From: Penelope Maddy (Defending the Axioms [2011], 1.3) |
| 17625 | If two mathematical themes coincide, that suggest a single deep truth [Maddy] |
| Full Idea: The fact that two apparently fruitful mathematical themes turn out to coincide makes it all the more likely that they're tracking a genuine strain of mathematical depth. | |
| From: Penelope Maddy (Defending the Axioms [2011], 5.3ii) |
| 17615 | Every infinite set of reals is either countable or of the same size as the full set of reals [Maddy] |
| Full Idea: One form of the Continuum Hypothesis is the claim that every infinite set of reals is either countable or of the same size as the full set of reals. | |
| From: Penelope Maddy (Defending the Axioms [2011], 2.4 n40) |
| 17618 | Set-theory tracks the contours of mathematical depth and fruitfulness [Maddy] |
| Full Idea: Our set-theoretic methods track the underlying contours of mathematical depth. ...What sets are, most fundamentally, is markers for these contours ...they are maximally effective trackers of certain trains of mathematical fruitfulness. | |
| From: Penelope Maddy (Defending the Axioms [2011], 3.4) | |
| A reaction: This seems to make it more like a map of mathematics than the actual essence of mathematics. |
| 17614 | The connection of arithmetic to perception has been idealised away in modern infinitary mathematics [Maddy] |
| Full Idea: Ordinary perceptual cognition is most likely involved in our grasp of elementary arithmetic, but ...this connection to the physical world has long since been idealized away in the infinitary structures of contemporary pure mathematics. | |
| From: Penelope Maddy (Defending the Axioms [2011], 2.3) | |
| A reaction: Despite this, Maddy's quest is for a 'naturalistic' account of mathematics. She ends up defending 'objectivity' (and invoking Tyler Burge), rather than even modest realism. You can't 'idealise away' the counting of objects. I blame Cantor. |
| 19724 | Belief is knowledge if it is true, certain, and obtained by a reliable process [Ramsey] |
| Full Idea: I have always said that a belief was knowledge if it was (i) true, (ii) certain, (iii) obtained by a reliable process. | |
| From: Frank P. Ramsey (Knowledge [1929]), quoted by Juan Comesaņa - Reliabilism 2 | |
| A reaction: Remarkable to be addressing the Gettier problem at that date, but Russell had flirted with the problem. Ramsey says the production of the belief must be reliable, rather than the justification for the belief. Note that he wants certainty. |
| 16736 | Explanation is generally to deduce it from something better known, which comes in degrees [Boyle] |
| Full Idea: Generally speaking, to render a reason of an effect or phenomenon is to deduce it from something else in nature more known than itself, and consequently there may be diverse kinds of degrees of explication of the same thing. | |
| From: Robert Boyle (Certain Physical Essays [1672], II:21), quoted by Robert Pasnau - Metaphysical Themes 1274-1671 23.4 | |
| A reaction: There is a picture of a real explanatory structure to nature, from which we pick bits that interest us for entirely pragmatic reasons. Boyle and I are as one on this matter. |
| 16737 | The best explanations get down to primary basics, but others go less deep [Boyle] |
| Full Idea: Explications be most satisfactory that show how the effect is produced by the more primitive affects of matter (bulk, shape and motion) but are not to be despised that deduce them from more familiar qualities such as heat, weight, fluidity, fermentation. | |
| From: Robert Boyle (Certain Physical Essays [1672], II:22), quoted by Robert Pasnau - Metaphysical Themes 1274-1671 23.4 | |
| A reaction: [Compressed, and continued from Idea 16736] So there is a causal structure, and the best explanations go to the bottom of it, but lesser explanations only go half way down. So a very skimpy explanation ('dormative power') is still an explanation. |