9 ideas
| 17884 | Mathematical set theory has many plausible stopping points, such as finitism, and predicativism [Koellner] |
| Full Idea: There are many coherent stopping points in the hierarchy of increasingly strong mathematical systems, starting with strict finitism, and moving up through predicativism to the higher reaches of set theory. | |
| From: Peter Koellner (On the Question of Absolute Undecidability [2006], Intro) |
| 17893 | 'Reflection principles' say the whole truth about sets can't be captured [Koellner] |
| Full Idea: Roughly speaking, 'reflection principles' assert that anything true in V [the set hierarchy] falls short of characterising V in that it is true within some earlier level. | |
| From: Peter Koellner (On the Question of Absolute Undecidability [2006], 2.1) |
| 17894 | We have no argument to show a statement is absolutely undecidable [Koellner] |
| Full Idea: There is at present no solid argument to the effect that a given statement is absolutely undecidable. | |
| From: Peter Koellner (On the Question of Absolute Undecidability [2006], 5.3) |
| 17890 | There are at least eleven types of large cardinal, of increasing logical strength [Koellner] |
| Full Idea: Some of the standard large cardinals (in order of increasing (logical) strength) are: inaccessible, Mahlo, weakly compact, indescribable, Erdös, measurable, strong, Wodin, supercompact, huge etc. (...and ineffable). | |
| From: Peter Koellner (On the Question of Absolute Undecidability [2006], 1.4) | |
| A reaction: [I don't understand how cardinals can have 'logical strength', but I pass it on anyway] |
| 17887 | PA is consistent as far as we can accept, and we expand axioms to overcome limitations [Koellner] |
| Full Idea: To the extent that we are justified in accepting Peano Arithmetic we are justified in accepting its consistency, and so we know how to expand the axiom system so as to overcome the limitation [of Gödel's Second Theorem]. | |
| From: Peter Koellner (On the Question of Absolute Undecidability [2006], 1.1) | |
| A reaction: Each expansion brings a limitation, but then you can expand again. |
| 17891 | Arithmetical undecidability is always settled at the next stage up [Koellner] |
| Full Idea: The arithmetical instances of undecidability that arise at one stage of the hierarchy are settled at the next. | |
| From: Peter Koellner (On the Question of Absolute Undecidability [2006], 1.4) |
| 23283 | Necessity implies possibility, but in experience it matters which comes first [Williams,B] |
| Full Idea: Any notion of necessity must carry with it a corresponding notion of impossibility, …but it can make a difference which one of them presents itself first and more naturally. | |
| From: Bernard Williams (Practical Necessity [1982], p.127) | |
| A reaction: I like this because it connects modality with experience, rather than with formal logic. It seems right that in life we immediately see either a necessity or an impossibility, and inferring the other case is an afterthought. |
| 21862 | Consciousness is based on 'I can', not on 'I think' [Merleau-Ponty] |
| Full Idea: Consciousness is in the first place not a matter of 'I think' but of 'I can'. | |
| From: Maurice Merleau-Ponty (Phenomenology of Perception [1945], p.159), quoted by Beth Lord - Spinoza's Ethics 2 'Sensation' | |
| A reaction: The point here (quoted during a discussion of Spinoza) is that you can't leave out the role of the body, which seems correct. |
| 20750 | The mind does not unite perceptions, because they flow into one another [Merleau-Ponty] |
| Full Idea: I do not have one perception, then another, and between them a link brought about by the mind. Rather, each perspective merges into the other [against a unified background]. | |
| From: Maurice Merleau-Ponty (Phenomenology of Perception [1945], p.329-30), quoted by Kevin Aho - Existentialism: an introduction 3 'Perceptual' | |
| A reaction: I take this to be another piece of evidence pointing to realism as the best explanation of experience. A problem for Descartes is what unites the sequence of thoughts. |