12 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. |
| 18088 | Intentionality is the mark of dispositions, not of the mental [Place] |
| Full Idea: My thesis is that intentionality is the mark, not of the mental, but of the dispositional. | |
| From: Ullin T. Place (Intentionality and the Physical: reply to Mumford [1999], 1) | |
| A reaction: An idea with few friends, but I really like it, because it offers the prospect of a unified account of physical nature and the mind/brain. It seems reasonable to say my mind is essentially a bunch of dispositions. Mind is representations + dispositions. |
| 4055 | It isn't obviously wicked to destroy a potential human being (e.g. an ununited egg and sperm) [Lockwood] |
| Full Idea: A week-old embryo without a brain may be a potential human being, but so are a sperm and an ovum that are about to meet in a dish, and it wouldn't be wicked to keep those apart. | |
| From: Michael Lockwood (When Does a Life Begin? [1985], p.19) | |
| A reaction: Sounds fine, but it may be a slippery slope. Is it acceptable to deny a place at music school to a potentially great musician? |
| 4054 | I may exist before I become a person, just as I exist before I become an adult [Lockwood] |
| Full Idea: It makes perfectly good sense to say that I existed before I became a person, just as I existed before I became an adult, or a philosopher. | |
| From: Michael Lockwood (When Does a Life Begin? [1985], p.13) | |
| A reaction: The word 'I' needs thought here. I was once a non-adult, but was I ever a non-person? 'Person' is not a clear concept, despite what many philosophers since Locke may think. |
| 4056 | If the soul is held to leave the body at brain-death, it should arrive at the time of brain-creation [Lockwood] |
| Full Idea: Any Christian who feels that body and soul go their separate ways at brain death ought in consistency to hold that they come together only at the point when whatever is destroyed at brain death first came into being. | |
| From: Michael Lockwood (When Does a Life Begin? [1985], p.24) | |
| A reaction: Hence Christians probably focus less on brain-death than do doctors and the rest of us. |
| 18089 | Dispositions are not general laws, but laws of the natures of individual entities [Place] |
| Full Idea: Dispositions are the substantive laws, not, as for Armstrong, of nature in general, but of the nature of individual entities whose dispositional properties they are. | |
| From: Ullin T. Place (Intentionality and the Physical: reply to Mumford [1999], 6) | |
| A reaction: [He notes that Nancy Cartwright 1989 agrees with him] I like this a lot. I tend to denegrate 'laws', because of their dubious ontological status, but this restores laws to the picture, in the place where they belong, in the stuff of the world. |