11 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. |
| 23035 | The good life aims at perfections, or absolute laws, or what is absolutely desirable [Green,TH] |
| Full Idea: The differentia of the good life …is controlled by the consciousness of there being some perfection which has to be fulfilled, some law which has to be obeyed, something absolutely desirable whatever the individual may for the time desire. | |
| From: T.H. Green (Prolegomena to Ethics [1882], p.134), quoted by John H. Muirhead - The Service of the State II | |
| A reaction: The 'perfection' suggests Plato, and the 'law' suggests Kant. The idea that something is 'absolutely desirable' is, I suspect, aimed at the utilitarians, who don't care what is desired. I'm no idealist, but have some sympathy with this idea. |
| 1460 | Religious experience deserves the same respect as our other key experiences, and is best called 'holy' [Taylor,AE, by PG] |
| Full Idea: We respect the religious experience of others in a similar way to our respect for their artistic or sense experiences, and the quality which makes them seem authentic can only be called 'holy'. | |
| From: report of A.E. Taylor (Vindication of Religion (extract) [1926], III) by PG - Db (ideas) |
| 23037 | People are improved by egalitarian institutions and habits [Green,TH] |
| Full Idea: Man has bettered himself through institutions and habits which tend to make the welfare of all the welfare of each. | |
| From: T.H. Green (Prolegomena to Ethics [1882], p.180), quoted by John H. Muirhead - The Service of the State II | |
| A reaction: I like this a lot. We underestimate how the best social values are promoted by the existence of enlightened institutions, rather than by preaching and teaching. Schools, law courts and churche embody their values. |
| 23043 | All talk of the progress of a nation must reduce to the progress of its individual members [Green,TH] |
| Full Idea: Our ultimate standard of worth is an ideal of personal worth. All other values are relative to personal values. To speak of any progress of a nation or society or mankind except as relative to some greater worth of persons is to use words without meaning. | |
| From: T.H. Green (Prolegomena to Ethics [1882], p.193), quoted by John H. Muirhead - The Service of the State II | |
| A reaction: Note that, pre-verificationism, a Victorian talks of plausible words actually being meaningless. This is a good statement of the core doctrine of liberalism. |