17 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. |
| 594 | Speusippus suggested underlying principles for every substance, and ended with a huge list [Speussipus, by Aristotle] |
| Full Idea: Speusippus suggested principles for each substance, including principles for numbers, magnitude and the soul. He thus arrived at no mean list of substances. | |
| From: report of Speussipus (thirty titles (lost) [c.367 BCE]) by Aristotle - Metaphysics 1028b |
| 19451 | When absorbed in deep reflection, is your reason in control, or is it you? [Feuerbach] |
| Full Idea: When, submerged in deep reflection, you forget both yourself and your surroundings, is it you who controls reason, or is it rather reason that controls and absorbs you? | |
| From: Ludwig Feuerbach (Introduction of 'Essence of Christianity' [1841], I) | |
| A reaction: A delightful question, even if it looks like a false dichotomy. I'm not sure what to make of 'me', if my reason can be subtracted from it. Aquinas was one the same wavelength here. |
| 19450 | Reason, love and will are the highest perfections and essence of man - the purpose of his life [Feuerbach] |
| Full Idea: Reason, love and power of will are perfections of man; they are his highest powers, his absolute essence in so far as he is man, the purpose of his existence. Man exists in order to think, love and will. | |
| From: Ludwig Feuerbach (Introduction of 'Essence of Christianity' [1841], I) | |
| A reaction: Feuerbach was a notable atheist, but adopts a religious style of language which modern atheists would find rather alien. Personally I love talk of ideals and perfections. Ideals have been discredited in modern times, but need a revival. |
| 19448 | Consciousness is said to distinguish man from animals - consciousness of his own species [Feuerbach] |
| Full Idea: What constitutes the essential difference between man and animal? The most simple, general, and most widely held answer to this question is consciousness. Consciousness is given only in the case of a being to whom his species ...is an object of thought. | |
| From: Ludwig Feuerbach (Introduction of 'Essence of Christianity' [1841], I) | |
| A reaction: Rather speculative. Since other species cohabit and breed only with their fellow species members, one might have thought they were aware of them. |
| 19454 | A God needs justice, kindness and wisdom, but those concepts don't depend on the concept of God [Feuerbach] |
| Full Idea: The concept of God depends on the concepts of justice, kindness and wisdom - a God who is not kind, not just, and not wise is no God. But these concepts do not depend on the concept of God. That a quality is possessed by God does not make it divine. | |
| From: Ludwig Feuerbach (Introduction of 'Essence of Christianity' [1841], II) | |
| A reaction: This is part of Feuerbach's argument for atheism, but if you ask for the source of our human concepts of justice, kindness and wisdom, no one, I would have thought, could cite God for the role. |
| 19452 | The nature of God is an expression of human nature [Feuerbach] |
| Full Idea: God is the manifestation of man's inner nature, his expressed self. | |
| From: Ludwig Feuerbach (Introduction of 'Essence of Christianity' [1841], II) | |
| A reaction: Even if you are a deeply committed theist, you have to concede some of this point. The perfections attributed to God are usually of human qualities. Leibniz, though, says that God has an infinity of perfection, mostly unknown to us. |
| 19453 | If love, goodness and personality are human, the God who is their source is anthropomorphic [Feuerbach] |
| Full Idea: If love, goodness, and personality are human determinations, the being which constitutes their source and ...their presupposition is also an anthropomorphism; so is the existence of God. | |
| From: Ludwig Feuerbach (Introduction of 'Essence of Christianity' [1841], II) | |
| A reaction: It is certainly a struggle for the imagination to grasp a being which is characterised by idealised versions of human virtues, and yet has an intrinsic nature which is utterly different from humanity. |
| 2632 | Speusippus said things were governed by some animal force rather than the gods [Speussipus, by Cicero] |
| Full Idea: Speusippus, following his uncle Plato, held that all things were governed by some kind of animal force, and tried to eradicate from our minds any notion of the gods. | |
| From: report of Speussipus (thirty titles (lost) [c.367 BCE]) by M. Tullius Cicero - On the Nature of the Gods ('De natura deorum') I.33 |
| 19455 | Today's atheism will tomorrow become a religion [Feuerbach] |
| Full Idea: What is regarded as atheism today will be religion tomorrow. | |
| From: Ludwig Feuerbach (Introduction of 'Essence of Christianity' [1841], II) | |
| A reaction: Modern critics of atheism frequently accuse it of being a new religion. I doubt whether Feuerbach is right, but it is a nice provocative idea. |
| 19449 | Religion is the consciousness of the infinite [Feuerbach] |
| Full Idea: Religion is the consciousness of the infinite. | |
| From: Ludwig Feuerbach (Introduction of 'Essence of Christianity' [1841], I) |