16 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. |
| 4042 | Metaphysics requires the idea of people (speakers) located in space and time [Davidson] |
| Full Idea: An intelligible metaphysics will assign a central place to the idea of people (= speakers) with a location in public space and time. | |
| From: Donald Davidson (The Method of Truth in Metaphysics [1977], §III) | |
| A reaction: The 'location' is the interesting bit, requiring people to be bodies, not abstractions. A big, plausible claim, but hard to prove. |
| 3654 | The pineal gland links soul to body, and unites the two symmetrical sides of the body [Descartes, by PG] |
| Full Idea: The soul is united with the body in just one place, a gland (the pineal) in the centre of the brain. It is placed so that its slightest movement will affect the passions, and it plays the essential role of uniting the two symmetrical sides of the body. | |
| From: report of René Descartes (The Passions of the Soul [1649], §31) by PG - Db (ideas) | |
| A reaction: See Idea 4862 for Spinoza's nice response to Descartes' proposal. If Descartes had followed brain research for the last four hundred years, at what point would he have wavered? If every single part of the brain seems to 'interact', dualism looks unlikely. |
| 4015 | For Descartes passions are God-given preservers of the mind-body union [Descartes, by Taylor,C] |
| Full Idea: Descartes sees passions not as opinions, but as functional devices that the Creator has designed for us to help preserve the body-soul substantial union. | |
| From: report of René Descartes (The Passions of the Soul [1649]) by Charles Taylor - Sources of the Self §8 | |
| A reaction: I wonder what Descartes would have made of the theory of evolution? |
| 4313 | Are there a few primary passions (say, joy, sadness and desire)? [Descartes, by Cottingham] |
| Full Idea: Descartes says there are six primary passions (wonder, love, hatred, desire, joy and sadness); Spinoza says there are just three (joy, sadness and desire). | |
| From: report of René Descartes (The Passions of the Soul [1649]) by John Cottingham - The Rationalists p.172 | |
| A reaction: A dubious project. However, it is now agreed that there are a few (six?) basic universal facial expressions, to which these passions may correspond. |
| 23989 | There are six primitive passions: wonder, love, hatred, desire, joy and sadness [Descartes, by Goldie] |
| Full Idea: Descartes said there are six primitive passions, namely wonder, love, hatred, desire, joy and sadness. The others are either species of these, or composed of them. | |
| From: report of René Descartes (The Passions of the Soul [1649], 353) by Peter Goldie - The Emotions 4 'Evidence' | |
| A reaction: [not sure about ref] It's a nice touch to add 'wonder', which doesn't make it onto anyone else's list. |
| 4041 | Sentences held true determine the meanings of the words they contain [Davidson] |
| Full Idea: Sentences held true (the linguistic representatives of beliefs) determine the meanings of the words they contain. | |
| From: Donald Davidson (The Method of Truth in Metaphysics [1977], §II) | |
| A reaction: Maybe. Historically, truth and belief presumably precede words and sentences. But words separate off from beliefs very easily. I'm not convinced. Words initiate language, not beliefs? |
| 20037 | Merely willing to walk leads to our walking [Descartes] |
| Full Idea: Our merely willing to walk has the consequence that our legs move and we walk. | |
| From: René Descartes (The Passions of the Soul [1649], 18), quoted by Rowland Stout - Action 1 'Volitionism' | |
| A reaction: Stout attributes this to Descartes' dualism, as if legs are separate from persons. Stout says the idea of a prior mental act is not usually now considered as part of an action, or even to exist at all. If the volition is intentional, there is a regress. |
| 16763 | We don't die because the soul departs; the soul departs because the organs cease functioning [Descartes] |
| Full Idea: We ought to hold, on the contrary, that the soul takes its leave when we die only because this heat ceases and the organs that bring about bodily movement decay. | |
| From: René Descartes (The Passions of the Soul [1649], I.5), quoted by Robert Pasnau - Metaphysical Themes 1274-1671 24.5 | |
| A reaction: This sounds like a pretty major change in our concept of death, given that we all now agree with Descartes. |
| 4016 | Descartes makes strength of will the central virtue [Descartes, by Taylor,C] |
| Full Idea: Descartes makes strength of will the central virtue. | |
| From: report of René Descartes (The Passions of the Soul [1649]) by Charles Taylor - Sources of the Self §8 | |
| A reaction: Presumably strength of will can serve evil ends, so this is a bit confusing. |