8 ideas
| 17833 | The first-order ZF axiomatisation is highly non-categorical [Hallett,M] |
| Full Idea: The first-order Sermelo-Fraenkel axiomatisation is highly non-categorical. | |
| From: Michael Hallett (Introduction to Zermelo's 1930 paper [1996], p.1213) |
| 17834 | Non-categoricity reveals a sort of incompleteness, with sets existing that the axioms don't reveal [Hallett,M] |
| Full Idea: The non-categoricity of the axioms which Zermelo demonstrates reveals an incompleteness of a sort, ....for this seems to show that there will always be a set (indeed, an unending sequence) that the basic axioms are incapable of revealing to be sets. | |
| From: Michael Hallett (Introduction to Zermelo's 1930 paper [1996], p.1215) | |
| A reaction: Hallett says the incompleteness concerning Zermelo was the (transfinitely) indefinite iterability of the power set operation (which is what drives the 'iterative conception' of sets). |
| 17837 | Zermelo allows ur-elements, to enable the widespread application of set-theory [Hallett,M] |
| Full Idea: Unlike earlier writers (such as Fraenkel), Zermelo clearly allows that there might be ur-elements (that is, objects other than the empty set, which have no members). Indeed he sees in this the possibility of widespread application of set-theory. | |
| From: Michael Hallett (Introduction to Zermelo's 1930 paper [1996], p.1217) |
| 17836 | The General Continuum Hypothesis and its negation are both consistent with ZF [Hallett,M] |
| Full Idea: In 1938, Gödel showed that ZF plus the General Continuum Hypothesis is consistent if ZF is. Cohen showed that ZF and not-GCH is also consistent if ZF is, which finally shows that neither GCH nor ¬GCH can be proved from ZF itself. | |
| From: Michael Hallett (Introduction to Zermelo's 1930 paper [1996], p.1217) |
| 8526 | We might treat both tropes and substances as fundamental, so we can't presume it is just tropes [Daly] |
| Full Idea: Since C.B. Martin accepts both tropes and substances as fundamental, the claim that tropes are the only fundamental constituents is a further, independent claim. | |
| From: Chris Daly (Tropes [1995], §4) | |
| A reaction: A dubious mode of argument. Martin may only make the claim because he is ignorant, of facts or of language. Why are some tropes perfectly similar? Is it the result of something more fundamental? |
| 8527 | More than one trope (even identical ones!) can occupy the same location [Daly] |
| Full Idea: More than one trope can occupy the same spatio-temporal location, and it even seems possible for a pair of exactly resembling tropes to occupy the same spatio-temporal location. | |
| From: Chris Daly (Tropes [1995], §6) | |
| A reaction: This may be the strongest objection to tropes. Being disc-shaped and red would occupy the same location. Aristotle's example of mixing white with white (Idea 557) would be the second case. Individuation of these 'particulars' is the problem. |
| 8528 | If tropes are linked by the existence of concurrence, a special relation is needed to link them all [Daly] |
| Full Idea: To explain how tropes form bundles, concurrence relations are invoked. But tropes F and G and a concurrence relation C don't ensure that F stands in C to G. So trope theory needs 'instantiation' relations (special relational tropes) after all. | |
| From: Chris Daly (Tropes [1995], §7) | |
| A reaction: Campbell presents relations as 'second-order' items dependent on tropes (Idea 8525), but that seems unclear. Daly's argument resembles Russell's (which he likes), that some sort of universal is inescapable. It also resembles Bradley's regress (7966). |
| 20653 | Six reduction levels: groups, lives, cells, molecules, atoms, particles [Putnam/Oppenheim, by Watson] |
| Full Idea: There are six 'reductive levels' in science: social groups, (multicellular) living things, cells, molecules, atoms, and elementary particles. | |
| From: report of H.Putnam/P.Oppenheim (Unity of Science as a Working Hypothesis [1958]) by Peter Watson - Convergence 10 'Intro' | |
| A reaction: I have the impression that fields are seen as more fundamental that elementary particles. What is the status of the 'laws' that are supposed to govern these things? What is the status of space and time within this picture? |