11 ideas
| 2626 | A philosopher is outside any community of ideas [Wittgenstein] |
| Full Idea: The philosopher is not a citizen of any community of ideas; that is what makes him a philosopher. | |
| From: Ludwig Wittgenstein (Zettel [1950], 455) | |
| A reaction: A bit surprising from the man who gave us 'language games' and 'private language argument'. |
| 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) |
| 6569 | 'This sentence is false' sends us in a looping search for its proposition [Wittgenstein, by Fogelin] |
| Full Idea: According to Wittgenstein, 'this sentence is false' sends us off on an endless, looping search for the proposition to be evaluated. | |
| From: report of Ludwig Wittgenstein (Zettel [1950], §691) by Robert Fogelin - Walking the Tightrope of Reason Ch.2 | |
| A reaction: Fogelin quotes this as one possible strategy for dealing with the Liar Paradox. It doesn't sound like much of a solution to the paradox, merely an account of why it is so annoying. Wittgenstein's challenge is that the Cretan can't state his problem. |
| 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. |
| 3790 | Causes of beliefs are irrelevant to their contents [Wittgenstein] |
| Full Idea: The causes of our belief in a proposition are indeed irrelevant to the question of what we believe. | |
| From: Ludwig Wittgenstein (Zettel [1950], i.437) | |
| A reaction: This should have nipped the causal theory of knowledge in the bud before it got started. Everyone has a different cause for their belief that 'it sometimes rains'. Cause is not justification. |
| 20957 | We don't choose our characters, yet we still claim credit for the actions our characters perform [Schelling] |
| Full Idea: Nobody has chosen their character; and yet this does not stop anybody attributing the action which follows from his character to themself as a free action. | |
| From: Friedrich Schelling (The Ages of the World [1810], I.93) | |
| A reaction: This pinpoints a very nice ambivalence about our attitudes to our own characters. We all have some pride and shame about who we are, without having chosed who we are. At least when we are young. But we make the bed we lie in. |