12 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) |
| 13230 | Particular essence is often captured by generality [Steiner,M] |
| Full Idea: Generality is often necessary for capturing the essence of a particular. | |
| From: Mark Steiner (Mathematical Explanation [1978], p.36) | |
| A reaction: The most powerful features of an entity are probably those which are universal, like intelligence or physical strength in a human. Those characteristics are powerful because they compete with the same characteristic in others (perhaps?). |
| 13229 | Maybe an instance of a generalisation is more explanatory than the particular case [Steiner,M] |
| Full Idea: Maybe to deduce a theorem as an instance of a generalization is more explanatory than to deduce it correctly. | |
| From: Mark Steiner (Mathematical Explanation [1978], p.32) | |
| A reaction: Steiner eventually comes down against this proposal, on the grounds that some proofs are too general, and hence too far away from the thing they are meant to explain. |
| 13231 | Explanatory proofs rest on 'characterizing properties' of entities or structure [Steiner,M] |
| Full Idea: My proposal is that an explanatory proof makes reference to the 'characterizing property' of an entity or structure mentioned in the theorem, where the proof depends on the property. If we substitute a different object, the theory collapses. | |
| From: Mark Steiner (Mathematical Explanation [1978], p.34) | |
| A reaction: He prefers 'characterizing property' to 'essence', because he is not talking about necessary properties, since all properties are necessary in mathematics. He is, in fact, reverting to the older notion of an essence, as the core power of the thing. |
| 6383 | Cause unites our picture of the universe; without it, mental and physical will separate [Davidson] |
| Full Idea: The concept of cause is what holds together our picture of the universe, a picture that would otherwise disintegrate into a diptych of the mental and the physical. | |
| From: Donald Davidson (Intro to 'Essays on Actions and Events' [1980], p.xi) | |
| A reaction: Davidson seems to be the one who put mental causation at the centre of philosophy. By then denying that there are any 'psycho-physical' laws, he seems to me to have re-opened the metaphysical gap he says he was trying to close. |
| 6385 | The causally strongest reason may not be the reason the actor judges to be best [Davidson] |
| Full Idea: I defend my causal view of action by arguing that a reason that is causally strongest need not be a reason deemed by the actor to provide the strongest (best) grounds for acting. | |
| From: Donald Davidson (Intro to 'Essays on Actions and Events' [1980], p.xii) | |
| A reaction: If I smoke a cigarette against my better judgement, it is not clear to me how the desire to smoke it, which overcomes my judgement not to smoke it, counts as the causally strongest 'reason'. We seem to have two different senses of 'reason' here. |
| 6384 | The notion of cause is essential to acting for reasons, intentions, agency, akrasia, and free will [Davidson] |
| Full Idea: My thesis is that the ordinary notion of cause is essential to understanding what it is to act with a reason, to have an intention to act, to be an agent, to act counter to one's own best judgement, or to act freely. | |
| From: Donald Davidson (Intro to 'Essays on Actions and Events' [1980], p.xi) | |
| A reaction: I cautiously agree, particularly with idea that causation is essential to acting as an agent. Since I believe 'free will' to be a complete delusion, that part of his thesis doesn't interest me. The hard part is understanding acting for a reason. |