13 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) |
| 19400 | Possibles demand existence, so as many of them as possible must actually exist [Leibniz] |
| Full Idea: From the conflict of all the possibles demanding existence, this at once follows, that there exists that series of things by which as many of them as possible exist. | |
| From: Gottfried Leibniz (Exigency to Exist in Essences [1690], p.91) | |
| A reaction: I'm in tune with a lot of Leibniz, but my head swims with this one. He seems to be a Lewisian about possible worlds - that they are concrete existing entities (with appetites!). Could Lewis include Leibniz's idea in his system? |
| 19401 | God's sufficient reason for choosing reality is in the fitness or perfection of possibilities [Leibniz] |
| Full Idea: The sufficient reason for God's choice can be found only in the fitness (convenance) or in the degree of perfection that the several worlds possess. | |
| From: Gottfried Leibniz (Exigency to Exist in Essences [1690], p.92) | |
| A reaction: The 'fitness' of a world and its 'perfection' seem very different things. A piece of a jigsaw can have wonderful fitness, without perfection. Occasionally you get that sinking feeling with metaphysicians that they just make it up. |
| 19402 | The actual universe is the richest composite of what is possible [Leibniz] |
| Full Idea: The actual universe is the collection of the possibles which forms the richest composite. | |
| From: Gottfried Leibniz (Exigency to Exist in Essences [1690], p.92) | |
| A reaction: 'Richest' for Leibniz means a maximum combination of existence, order and variety. It's rather like picking the best starting team from a squad of footballers. |
| 20482 | Virtue inspires Stoics, but I want a good temperament [Montaigne] |
| Full Idea: What Stoics did from virtue I teach myself to do from temperament. | |
| From: Michel de Montaigne (III.10 On Restraining your Will [1580], p.1153) | |
| A reaction: I take this to be an Aristotelian criticism of Stoicism. They venerate virtue above everything, but Aristotle says you must integrate virtue into your very being, so that right actions flow from you, with very little need for premeditation. |
| 20480 | There is not much point in only becoming good near the end of your life [Montaigne] |
| Full Idea: It is almost better never to become a good man at all than to do so tardily, understanding how to live when you have no life left. | |
| From: Michel de Montaigne (III.10 On Restraining your Will [1580], p.1142) | |
| A reaction: A very nice perspective, which I don't recall Aristotle mentioning. It does, though, reinforce Aristotle's belief that early training is essential. |
| 20481 | Nothing we say can be worse than unsaying it in the face of authority [Montaigne] |
| Full Idea: Nothing which a gentleman says can seem worse than the shame of his unsaying it under duress from authority. | |
| From: Michel de Montaigne (III.10 On Restraining your Will [1580], p.1153) | |
| A reaction: The point is that you have to fight every day for free speech, because no matter what the law says, there are always people in power who want to shut you up. |
| 20479 | People at home care far more than soldiers risking death about the outcome of wars [Montaigne] |
| Full Idea: How many soldiers put themselves at risk every day in wars which they care little about, rushing into danger in battles the loss of which will not make them lose a night's sleep. Meanwhile a man at home is more passionate about the war than the soldier. | |
| From: Michel de Montaigne (III.10 On Restraining your Will [1580], p.1139) | |
| A reaction: It depends whether you are a mercenary (which the majority probably were in 1680), and what are the implications of defeat. |