13 ideas
| 9193 | ZF set theory has variables which range over sets, 'equals' and 'member', and extensionality [Dummett] |
| Full Idea: ZF set theory is a first-order axiomatization. Variables range over sets, there are no second-order variables, and primitive predicates are just 'equals' and 'member of'. The axiom of extensionality says sets with the same members are identical. | |
| From: Michael Dummett (The Philosophy of Mathematics [1998], 7) | |
| A reaction: If the eleven members of the cricket team are the same as the eleven members of the hockey team, is the cricket team the same as the hockey team? Our cricket team is better than our hockey team, so different predicates apply to them. |
| 9194 | The main alternative to ZF is one which includes looser classes as well as sets [Dummett] |
| Full Idea: The main alternative to ZF is two-sorted theories, with some variables ranging over classes. Classes have more generous existence assumptions: there is a universal class, containing all sets, and a class containing all ordinals. Classes are not members. | |
| From: Michael Dummett (The Philosophy of Mathematics [1998], 7.1.1) | |
| A reaction: My intuition is to prefer strict systems when it comes to logical theories. The whole point is precision. Otherwise we could just think about things, and skip all this difficult symbolic stuff. |
| 9195 | Intuitionists reject excluded middle, not for a third value, but for possibility of proof [Dummett] |
| Full Idea: It must not be concluded from the rejection of excluded middle that intuitionistic logic operates with three values: true, false, and neither true nor false. It does not make use of true and false, but only with a construction being a proof. | |
| From: Michael Dummett (The Philosophy of Mathematics [1998], 8.1) | |
| A reaction: This just sounds like verificationism to me, with all its problems. It seems to make speculative statements meaningless, which can't be right. Realism has lots of propositions which are assumed to be true or false, but also unknowable. |
| 9186 | First-order logic concerns objects; second-order adds properties, kinds, relations and functions [Dummett] |
| Full Idea: First-order logic is distinguished by generalizations (quantification) only over objects: second-order logic admits generalizations or quantification over properties or kinds of objects, and over relations between them, and functions defined over them. | |
| From: Michael Dummett (The Philosophy of Mathematics [1998], 3.1) | |
| A reaction: Second-order logic was introduced by Frege, but is (interestingly) rejected by Quine, because of the ontological commitments involved. I remain unconvinced that quantification entails ontological commitment, so I'm happy. |
| 9187 | Logical truths and inference are characterized either syntactically or semantically [Dummett] |
| Full Idea: There are two ways of characterizing logical truths and correct inference. Proof-theoretic or syntactic characterizations, if the formalization admits of proof or derivation; and model-theoretic or semantic versions, being true in all interpretations. | |
| From: Michael Dummett (The Philosophy of Mathematics [1998], 3.1) | |
| A reaction: Dummett calls this distinction 'fundamental'. The second one involves truth, and hence meaning, where the first one just responds to rules. ..But how can you have a notion of correctly following a rule, without a notion of truth? |
| 9191 | Ordinals seem more basic than cardinals, since we count objects in sequence [Dummett] |
| Full Idea: It can be argued that the notion of ordinal numbers is more fundamental than that of cardinals. To count objects, we must count them in sequence. ..The theory of ordinals forms the substratum of Cantor's theory of cardinals. | |
| From: Michael Dummett (The Philosophy of Mathematics [1998], 5) | |
| A reaction: Depends what you mean by 'fundamental'. I would take cardinality to be psychologically prior ('that is a lot of sheep'). You can't order people by height without first acquiring some people with differing heights. I vote for cardinals. |
| 9192 | The number 4 has different positions in the naturals and the wholes, with the same structure [Dummett] |
| Full Idea: The number 4 cannot be characterized solely by its position in a system, because it has different positions in the system of natural numbers and that of the positive whole numbers, whereas these systems have the very same structure. | |
| From: Michael Dummett (The Philosophy of Mathematics [1998], 6.1) | |
| A reaction: Dummett seems to think this is fairly decisive against structuralism. There is also the structure of the real numbers. We will solve this by saying that the wholes are abstracted from the naturals, which are abstracted from the reals. Job done. |
| 13795 | Properties only have identity in the context of their contraries [Elder] |
| Full Idea: The very being, the identity, of any property consists at least in part in its contrasting as it does with its own proper contraries. | |
| From: Crawford L. Elder (Real Natures and Familiar Objects [2004], 2.4) | |
| A reaction: See Elder for the details of this, but the idea that properties can only be individuated contextually sounds promising. |
| 13798 | Maybe we should give up the statue [Elder] |
| Full Idea: Some contemporary metaphysicians infer that one of the objects must go, namely, the statue. | |
| From: Crawford L. Elder (Real Natures and Familiar Objects [2004], 7.2) | |
| A reaction: [He cites Zimmerman 1995] This looks like a recipe for creating a vast gulf between philosophers and the rest of the population. If it is right, it makes the true ontology completely useless in understanding our daily lives. |
| 13797 | The loss of an essential property means the end of an existence [Elder] |
| Full Idea: The loss of any essential property must amount to the end of an existence. | |
| From: Crawford L. Elder (Real Natures and Familiar Objects [2004], 3) | |
| A reaction: This is orthodoxy for essentialists, and I presume that Aristotle would agree, but I have a problem with the essence of a great athlete, who then grows old. Must we say that they lose their identity-as-an-athlete? |
| 13794 | Essential properties by nature occur in clusters or packages [Elder] |
| Full Idea: Essential properties by nature occur in clusters or packages. | |
| From: Crawford L. Elder (Real Natures and Familiar Objects [2004], 2.2) | |
| A reaction: Elder proposes this as his test for the essentialness of a property - his Test of Flanking Uniformities. A nice idea. |
| 13796 | Essential properties are bound together, and would be lost together [Elder] |
| Full Idea: The properties of any essential nature are bound together....[122] so any case in which one of our envisioned familiar objects loses one of its essential properties will be a case in which it loses several. | |
| From: Crawford L. Elder (Real Natures and Familiar Objects [2004], 3) | |
| A reaction: This sounds like a fairly good generalisation rather than a necessary truth. Is there a natural selection for properties, so that only the properties which are able to bind to others to form teams are able to survive and flourish? |
| 7903 | The six perfections are giving, morality, patience, vigour, meditation, and wisdom [Nagarjuna] |
| Full Idea: The six perfections are of giving, morality, patience, vigour, meditation, and wisdom. | |
| From: Nagarjuna (Mahaprajnaparamitashastra [c.120], 88) | |
| A reaction: What is 'morality', if giving is not part of it? I like patience and vigour being two of the virtues, which immediately implies an Aristotelian mean (which is always what is 'appropriate'). |