20 ideas
| 14001 | People who use science to make philosophical points don't realise how philosophical science is [Markosian] |
| Full Idea: When people give arguments from scientific theories to philosophical conclusions, there is usually a good deal of philosophy built into the relevant scientific theories. | |
| From: Ned Markosian (A Defense of Presentism [2004], 3.9) | |
| A reaction: I love this remark, being thoroughly fed up with knowledgeable scientists who are naďve about philosophy, and think their current theory demolishes long-lasting aporiai. They are up to their necks in philosophy. |
| 13991 | Presentism has the problem that if Socrates ceases to exist, so do propositions about him [Markosian] |
| Full Idea: Presentism has a problem with singular propositions about non-present objects. ...When Socrates popped out of existence, according to Presentism, all those singular propositions about him also popped out of existence. | |
| From: Ned Markosian (A Defense of Presentism [2004], 2.1) | |
| A reaction: He seems to treat propositions in a Russellian way, as things which exist independently of thinkers, which I struggle to grasp. Markosian offers various strategies for this [§3.5]. |
| 11022 | Gentzen introduced a natural deduction calculus (NK) in 1934 [Gentzen, by Read] |
| Full Idea: Gentzen introduced a natural deduction calculus (NK) in 1934. | |
| From: report of Gerhard Gentzen (works [1938]) by Stephen Read - Thinking About Logic Ch.8 |
| 11065 | The inferential role of a logical constant constitutes its meaning [Gentzen, by Hanna] |
| Full Idea: Gentzen argued that the inferential role of a logical constant constitutes its meaning. | |
| From: report of Gerhard Gentzen (works [1938]) by Robert Hanna - Rationality and Logic 5.3 | |
| A reaction: Possibly inspired by Wittgenstein's theory of meaning as use? This idea was the target of Prior's famous connective 'tonk', which has the role of implying anything you like, proving sentences which are not logical consequences. |
| 11023 | The logical connectives are 'defined' by their introduction rules [Gentzen] |
| Full Idea: The introduction rules represent, as it were, the 'definitions' of the symbols concerned, and the elimination rules are no more, in the final analysis, than the consequences of these definitions. | |
| From: Gerhard Gentzen (works [1938]), quoted by Stephen Read - Thinking About Logic Ch.8 | |
| A reaction: If an introduction-rule (or a truth table) were taken as fixed and beyond dispute, then it would have the status of a definition, since there would be nothing else to appeal to. So is there anything else to appeal to here? |
| 11213 | Each logical symbol has an 'introduction' rule to define it, and hence an 'elimination' rule [Gentzen] |
| Full Idea: To every logical symbol there belongs precisely one inference figure which 'introduces' the symbol ..and one which 'eliminates' it. The introductions represent the 'definitions' of the symbols concerned, and eliminations are consequences of these. | |
| From: Gerhard Gentzen (works [1938], II.5.13), quoted by Ian Rumfitt - "Yes" and "No" III | |
| A reaction: [1935 paper] This passage is famous, in laying down the basics of natural deduction systems of logic (ones using only rules, and avoiding axioms). Rumfitt questions whether Gentzen's account gives the sense of the connectives. |
| 13832 | Natural deduction shows the heart of reasoning (and sequent calculus is just a tool) [Gentzen, by Hacking] |
| Full Idea: Gentzen thought that his natural deduction gets at the heart of logical reasoning, and used the sequent calculus only as a convenient tool for proving his chief results. | |
| From: report of Gerhard Gentzen (Investigations into Logical Deduction [1935]) by Ian Hacking - What is Logic? §05 |
| 10067 | Gentzen proved the consistency of arithmetic from assumptions beyond arithmetic [Gentzen, by Musgrave] |
| Full Idea: Gentzen proved the consistency of arithmetic from assumptions which transcend arithmetic. | |
| From: report of Gerhard Gentzen (works [1938]) by Alan Musgrave - Logicism Revisited §5 | |
| A reaction: This does not contradict Gödel's famous result, but reinforces it. The interesting question is what assumptions Gentzen felt he had to make. |
| 14002 | Possible worlds must be abstract, because two qualitatively identical worlds are just one world [Markosian] |
| Full Idea: Possible worlds are just abstract objects that play a certain role in philosophers' talk about modality. They are ways things could be. That's why there are no two abstract possible worlds which are qualitatively identical. They count as one world. | |
| From: Ned Markosian (A Defense of Presentism [2004], 3.10) | |
| A reaction: Brilliant! This looks like the best distinction between concrete and abstract. If two concreta are identical they remain two; if two abstracta are identical they are one (like numbers, or logical connectives with the same truth table). |
| 20653 | Six reduction levels: groups, lives, cells, molecules, atoms, particles [Putnam/Oppenheim, by Watson] |
| Full Idea: There are six 'reductive levels' in science: social groups, (multicellular) living things, cells, molecules, atoms, and elementary particles. | |
| From: report of H.Putnam/P.Oppenheim (Unity of Science as a Working Hypothesis [1958]) by Peter Watson - Convergence 10 'Intro' | |
| A reaction: I have the impression that fields are seen as more fundamental that elementary particles. What is the status of the 'laws' that are supposed to govern these things? What is the status of space and time within this picture? |
| 14000 | 'Grabby' truth conditions first select their object, unlike 'searchy' truth conditions [Markosian] |
| Full Idea: We can talk of 'grabby' truth conditions (where an object is grabbed before predication) and 'searchy' truth conditions (where the object is included in what is being asserted). | |
| From: Ned Markosian (A Defense of Presentism [2004], 3.8) | |
| A reaction: [He credits Tom Ryckman with the terminology] I am inclined to think that the whole of language is 'searchy', even when it appears to be blatantly 'grabby'. Even ostensive reference is an act of hope rather than certainty. |
| 13990 | Presentism is the view that only present objects exist [Markosian] |
| Full Idea: According to Presentism, if we were to make an accurate list of all the things that exist (within the range of our most unrestricted quantifiers) there would not be a single non-present object on the list. | |
| From: Ned Markosian (A Defense of Presentism [2004], 1) | |
| A reaction: An immediate problem that needs examing is what constitutes an 'object'. It had better not range over time (like an journey). It would be hard to fit a description like 'the oldest man in England'. |
| 13992 | Presentism says if objects don't exist now, we can't have attitudes to them or relations with them [Markosian] |
| Full Idea: If there are no non-present objects (according to Presentism), then no one can now stand in any relation to any non-present object. You cannot now 'admire' Socrates, and no present event has a causal relation to Washington crossing the Delaware. | |
| From: Ned Markosian (A Defense of Presentism [2004], 2.2) | |
| A reaction: You can have an overlapping causal chain that gets you back to Washington, and a causal chain can connect Socrates to our thoughts about him (as in baptismal reference). A simple reply needs an 'overlap' though. |
| 13994 | Presentism seems to entail that we cannot talk about other times [Markosian] |
| Full Idea: It is very natural to talk about times, ...but Presentism seems to entail that we never say anything about any such times. | |
| From: Ned Markosian (A Defense of Presentism [2004], 2.4) | |
| A reaction: I'm beginning to think that Markosian is in the grips of a false notion of proposition, as something that exists independently of thinkers, and is entailed by the facts and objects of reality. This is not what language does. |
| 13995 | Serious Presentism says things must exist to have relations and properties; Unrestricted version denies this [Markosian] |
| Full Idea: Mark Hinchliff distinguishes between 'Serious' Presentism (objects only have relations and properties when they exist) and 'Unrestricted' Presentism (objects can have relations and properties even when they don't exist). | |
| From: Ned Markosian (A Defense of Presentism [2004], 3.1) | |
| A reaction: [Hinchliff 1996:124-6] Markosian votes for the Serious version, as being the only true Presentism. I think he is muddling language and reality, predicates and properties. |
| 13996 | Maybe Presentists can refer to the haecceity of a thing, after the thing itself disappears [Markosian] |
| Full Idea: Some Presentists (such as Adams) believe that a haecceity (a property unique to some entity) continues to exist even after its object ceases to exist. A sentence about Socrates still expresses a proposition, about 'Socraticity'. | |
| From: Ned Markosian (A Defense of Presentism [2004], 3.4) | |
| A reaction: [Adams 1986] This is rather puzzling. In what sense could a haecceity 'exist' to be referred to? Existence, but not as we know it, Jim. This smacks of medieval theology. |
| 13997 | Maybe Presentists can paraphrase singular propositions about the past [Markosian] |
| Full Idea: Maybe Presentists can paraphrase singular propositions about the past, into purely general past- and future-tensed sentences. | |
| From: Ned Markosian (A Defense of Presentism [2004], 3.5) | |
| A reaction: I'm not clear why Markosian worries about singular propositions, but is happy with general ones. Surely the latter refer as much as the former to what doesn't exist? Markosian objects that the paraphrase has a different meaning. |
| 13993 | Special Relativity denies the absolute present which Presentism needs [Markosian] |
| Full Idea: The objection to Presentism from Special Relativity is this: 1) Relativity is true, 2) so there is no absolute simultaneity, 3) so there is no absolute presentness, but 4) Presentism entails absolute presentness, so 5) Presentism is false. | |
| From: Ned Markosian (A Defense of Presentism [2004], 3.9) | |
| A reaction: I don't accept this objection. There may be accounts that can give Relativity one present (Idea 12689-90). Maybe Einstein was too instrumentalist in his account. Maybe we can have Presentism with multiple present moments. |
| 13998 | Objects in the past, like Socrates, are more like imaginary objects than like remote spatial objects [Markosian] |
| Full Idea: Maybe putative non-present objects like Socrates have more in common with putative non-actual objects like Santa Claus than they have in common with objects located elsewhere in space, like Alpha Centauri. | |
| From: Ned Markosian (A Defense of Presentism [2004], 3.7) | |
| A reaction: We can see Alpha Centauri, so we need an example beyond some 'event horizon'. He credits Arthur Prior with this line of thought. He seems to me to drift towards a Descriptive Theory of Reference (shock!). Does the nature of reference change with death? |
| 13999 | People are mistaken when they think 'Socrates was a philosopher' says something [Markosian] |
| Full Idea: People sometimes think that 'Socrates was a philosopher' expresses something like a true, singular proposition about Socrates. They're making a mistake, but still, this explains why they think it is true. | |
| From: Ned Markosian (A Defense of Presentism [2004], 3.8) | |
| A reaction: A classic error theory, about our talk of the past. Personally I would say that the sentence really is true, and that needing a tangible object to refer to is a totally bogus requirement. 'I wonder if there are any scissors in the house?' |