15 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) |
| 22445 | Morality shows murder is wrong, but not what counts as a murder [Foot] |
| Full Idea: While one can determine from the concept of morality that there is an objection to murder one cannot determine completely what will count as murder. | |
| From: Philippa Foot (Morality and Art [1972], p.7) | |
| A reaction: She then refers to abortion, but there are military and criminal problem cases, and killings by neglect or side effect. |
| 22444 | A moral system must deal with the dangers and benefits of life [Foot] |
| Full Idea: A moral system seems necessarily to be one aimed at removing particular dangers and securing certain benefits. | |
| From: Philippa Foot (Morality and Art [1972], p.6) | |
| A reaction: I thoroughly approve of this approach to morality, which anchors it in real life, rather than in ideals or principles of reason. |
| 22447 | Saying something 'just is' right or wrong creates an illusion of fact and objectivity [Foot] |
| Full Idea: When we say that something 'just is' right or wrong we want to give the impression of some kind of fact or authority standing behind our words, ...maintaining the trappings of objectivity though the substance is not there. | |
| From: Philippa Foot (Morality and Art [1972], p.9) | |
| A reaction: Foot favours the idea that such a claim must depend on reasons, and that the reasons arise out of actual living. She's right. |
| 22448 | We sometimes just use the word 'should' to impose a rule of conduct on someone [Foot] |
| Full Idea: It would be more honest to recognise that the 'should' of moral judgement is sometimes merely an instrument by which we (for our own very good reasons) try to impose a rule of conduct even on the uncaring man? | |
| From: Philippa Foot (Morality and Art [1972], p.18) | |
| A reaction: This is a good example, I think, of the ordinary language tradition that Foot grew up in. We load a word like 'should' with a mystical power, but the situations in which it is actually used bring us back down to earth. |
| 22446 | In the case of something lacking independence, calling it a human being is a matter of choice [Foot] |
| Full Idea: In the problem of abortion there is a genuine choice as to whether or not to count as a human being, with the rights of a human being, what would become a human being but is not yet capable of independent life. | |
| From: Philippa Foot (Morality and Art [1972], p.7) | |
| A reaction: There must be some basis for the choice. We can't call a dead person a human being. Choosing to call a tiny zygote a human being seems very implausible. Pre-viability strikes me as implausible. |
| 17402 | Mendeleev saw three principles in nature: matter, force and spirit (where the latter seems to be essence) [Mendeleev, by Scerri] |
| Full Idea: Mendeleev rejected one unifying principles in favour of three basic components of nature: matter (substance), force (energy), and spirit (soul). 'Spirit' is said to be what we now mean by essentialism - what is irreducibly peculiar to the object. | |
| From: report of Dmitri Mendeleev (The Principles of Chemistry [1870]) by Eric R. Scerri - The Periodic Table 04 'Making' |
| 17399 | Elements don't survive in compounds, but the 'substance' of the element does [Mendeleev] |
| Full Idea: Neither mercury as a metal nor oxygen as a gas is contained in mercury oxide; it only contains the substance of the elements, just as steam only contains the substance of ice. | |
| From: Dmitri Mendeleev (The Principles of Chemistry [1870], I:23), quoted by Eric R. Scerri - The Periodic Table 04 'Nature' | |
| A reaction: [1889 edn] Scerri glosses the word 'substance' as meaning essence. |
| 17400 | Mendeleev focused on abstract elements, not simple substances, so he got to their essence [Mendeleev, by Scerri] |
| Full Idea: Because he was attempting to classify abstract elements, not simple substances, Mendeleev was not misled by nonessential chemical properties. | |
| From: report of Dmitri Mendeleev (The Principles of Chemistry [1870]) by Eric R. Scerri - The Periodic Table 04 'Making' | |
| A reaction: I'm not fully clear about this, but I take it that Mendeleev stood back from the messy observations, and tried to see the underlying simpler principles. 'Simple substances' were ones that had not so far been decomposed. |
| 17401 | Mendeleev had a view of elements which allowed him to overlook some conflicting observations [Mendeleev] |
| Full Idea: His view of elements allowed Mendeleev to maintain the validity of the periodic table even in instances where observational evidence seemed to point against it. | |
| From: Dmitri Mendeleev (The Principles of Chemistry [1870]), quoted by Eric R. Scerri - The Periodic Table 04 'Making' | |
| A reaction: Mendeleev seems to have focused on abstract essences of elements, rather than on the simplest substances they had so far managed to isolate. |