10 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) |
| 22320 | An 'object' is just what can be referred to without possible non-existence [Wittgenstein] |
| Full Idea: What I once called 'objects', simples, were simply what I could refer to without running the risk of their possible non-existence. | |
| From: Ludwig Wittgenstein (Philosophical Remarks [1930], p.72), quoted by Michael Potter - The Rise of Analytic Philosophy 1879-1930 52 'Simp' | |
| A reaction: For most of us, you can refer to something because you take it to be an object. For these Fregean influenced guys (e.g. Hale) something is an object because you can refer to it. Why don't they use 'object*' for their things? |
| 18283 | Language pictures the essence of the world [Wittgenstein] |
| Full Idea: The essence of language is a picture of the essence of the world. | |
| From: Ludwig Wittgenstein (Philosophical Remarks [1930], p.85), quoted by J. Alberto Coffa - The Semantic Tradition from Kant to Carnap 17 | |
| A reaction: Hence for a long time the study of language seemed to be the way to do metaphysics. Now they study mathematical logic, with the same hope. |
| 18282 | You can't believe it if you can't imagine a verification for it [Wittgenstein] |
| Full Idea: It isn't possible to believe something for which you cannot imagine some kind of verification. | |
| From: Ludwig Wittgenstein (Philosophical Remarks [1930], p.200), quoted by J. Alberto Coffa - The Semantic Tradition from Kant to Carnap 13 'Constr' | |
| A reaction: In 1930 LW was calling this his 'old principle'. As it stands here it is too vague to assert very much. |
| 13440 | Causation is the power of one property to produce another, and this gives time its direction [Esfeld] |
| Full Idea: The metaphysics of causation in terms of powers is linked with an intrinsic direction of time. There is a causal connection if an F-property produces a G. One can argue that causation thus is the basis for the direction of time. | |
| From: Michael Esfeld (Humean metaphysics vs metaphysics of Powers [2010], 7.2) | |
| A reaction: I think this is my preferred metaphysic - that both time and causation are primitive, but the direction of time is the result of the causal process. Viewing some new world, we would just say that time went in whichever direction the causation went. |