31 ideas
| 14611 | Metaphysics should avoid talk of past, present or future [Smart] |
| Full Idea: Metaphysics should not be cosmically parochial. It should eschew tensed languages. | |
| From: J.J.C. Smart (The Tenseless Theory of Time [2008], 1) | |
| A reaction: This is quite an engaging reason to be an eternalist (or B-theorist) about time. Presumably we can still believe in tensed time, as long as we recognise that metaphysics itself is a timeless subject. |
| 17070 | Coherence is consilience, simplicity, analogy, and fitting into a web of belief [Smart] |
| Full Idea: I shall make use of the admittedly imprecise notions of consilience, simplicity, analogy and fitting into a web of belief, or in short of 'coherence'. | |
| From: J.J.C. Smart (Explanation - Opening Address [1990], p.06) | |
| A reaction: Coherence sounds like a family of tests, rather than a single unified concept. I still like coherence, though. |
| 17072 | We need comprehensiveness, as well as self-coherence [Smart] |
| Full Idea: Not mere self-coherence, but comprehensiveness belongs to the notion of coherence. | |
| From: J.J.C. Smart (Explanation - Opening Address [1990], p.07) |
| 10146 | Cantor's theories needed the Axiom of Choice, but it has led to great controversy [Feferman/Feferman] |
| Full Idea: The Axiom of Choice is a pure existence statement, without defining conditions. It was necessary to provide a foundation for Cantor's theory of transfinite cardinals and ordinal numbers, but its nonconstructive character engendered heated controversy. | |
| From: Feferman / Feferman (Alfred Tarski: life and logic [2004], Int I) |
| 10147 | The Axiom of Choice is consistent with the other axioms of set theory [Feferman/Feferman] |
| Full Idea: In 1938 Gödel proved that the Axiom of Choice is consistent with the other axioms of set theory. | |
| From: Feferman / Feferman (Alfred Tarski: life and logic [2004], Int I) | |
| A reaction: Hence people now standardly accept ZFC, rather than just ZF. |
| 10150 | The Trichotomy Principle is equivalent to the Axiom of Choice [Feferman/Feferman] |
| Full Idea: The Trichotomy Principle (any number is less, equal to, or greater than, another number) turned out to be equivalent to the Axiom of Choice. | |
| From: Feferman / Feferman (Alfred Tarski: life and logic [2004], Int I) | |
| A reaction: [He credits Sierpinski (1918) with this discovery] |
| 10148 | Axiom of Choice: a set exists which chooses just one element each of any set of sets [Feferman/Feferman] |
| Full Idea: Zermelo's Axiom of Choice asserts that for any set of non-empty sets that (pairwise) have no elements in common, then there is a set that 'simultaneously chooses' exactly one element from each set. Note that this is an existential claim. | |
| From: Feferman / Feferman (Alfred Tarski: life and logic [2004], Int I) | |
| A reaction: The Axiom is now widely accepted, after much debate in the early years. Even critics of the Axiom turn out to be relying on it. |
| 10149 | Platonist will accept the Axiom of Choice, but others want criteria of selection or definition [Feferman/Feferman] |
| Full Idea: The Axiom of Choice seems clearly true from the Platonistic point of view, independently of how sets may be defined, but is rejected by those who think such existential claims must show how to pick out or define the object claimed to exist. | |
| From: Feferman / Feferman (Alfred Tarski: life and logic [2004], Int I) | |
| A reaction: The typical critics are likely to be intuitionists or formalists, who seek for both rigour and a plausible epistemology in our theory. |
| 10158 | A structure is a 'model' when the axioms are true. So which of the structures are models? [Feferman/Feferman] |
| Full Idea: A structure is said to be a 'model' of an axiom system if each of its axioms is true in the structure (e.g. Euclidean or non-Euclidean geometry). 'Model theory' concerns which structures are models of a given language and axiom system. | |
| From: Feferman / Feferman (Alfred Tarski: life and logic [2004], Int V) | |
| A reaction: This strikes me as the most interesting aspect of mathematical logic, since it concerns the ways in which syntactic proof-systems actually connect with reality. Tarski is the central theoretician here, and his theory of truth is the key. |
| 10162 | Tarski and Vaught established the equivalence relations between first-order structures [Feferman/Feferman] |
| Full Idea: In the late 1950s Tarski and Vaught defined and established basic properties of the relation of elementary equivalence between two structures, which holds when they make true exactly the same first-order sentences. This is fundamental to model theory. | |
| From: Feferman / Feferman (Alfred Tarski: life and logic [2004], Int V) | |
| A reaction: This is isomorphism, which clarifies what a model is by giving identity conditions between two models. Note that it is 'first-order', and presumably founded on classical logic. |
| 10160 | Löwenheim-Skolem says if the sentences are countable, so is the model [Feferman/Feferman] |
| Full Idea: The Löwenheim-Skolem Theorem, the earliest in model theory, states that if a countable set of sentences in a first-order language has a model, then it has a countable model. | |
| From: Feferman / Feferman (Alfred Tarski: life and logic [2004], Int V) | |
| A reaction: There are 'upward' (sentences-to-model) and 'downward' (model-to-sentences) versions of the theory. |
| 10159 | Löwenheim-Skolem Theorem, and Gödel's completeness of first-order logic, the earliest model theory [Feferman/Feferman] |
| Full Idea: Before Tarski's work in the 1930s, the main results in model theory were the Löwenheim-Skolem Theorem, and Gödel's establishment in 1929 of the completeness of the axioms and rules for the classical first-order predicate (or quantificational) calculus. | |
| From: Feferman / Feferman (Alfred Tarski: life and logic [2004], Int V) |
| 10161 | If a sentence holds in every model of a theory, then it is logically derivable from the theory [Feferman/Feferman] |
| Full Idea: Completeness is when, if a sentences holds in every model of a theory, then it is logically derivable from that theory. | |
| From: Feferman / Feferman (Alfred Tarski: life and logic [2004], Int V) |
| 10156 | 'Recursion theory' concerns what can be solved by computing machines [Feferman/Feferman] |
| Full Idea: 'Recursion theory' is the subject of what can and cannot be solved by computing machines | |
| From: Feferman / Feferman (Alfred Tarski: life and logic [2004], Ch.9) | |
| A reaction: This because 'recursion' will grind out a result step-by-step, as long as the steps will 'halt' eventually. |
| 10155 | Both Principia Mathematica and Peano Arithmetic are undecidable [Feferman/Feferman] |
| Full Idea: In 1936 Church showed that Principia Mathematica is undecidable if it is ω-consistent, and a year later Rosser showed that Peano Arithmetic is undecidable, and any consistent extension of it. | |
| From: Feferman / Feferman (Alfred Tarski: life and logic [2004], Int IV) |
| 17073 | I simply reject evidence, if it is totally contrary to my web of belief [Smart] |
| Full Idea: The simplest way of fitting the putative observed phenomena of telepathy or clairvoyance into my web of belief is to refuse to take them at face value. | |
| From: J.J.C. Smart (Explanation - Opening Address [1990], p.07-8) | |
| A reaction: Love it. It is very disconcerting for the sceptical naturalist to be faced with adamant claims that the paranormal has occurred, but my response is exactly the same as Smart's. I reject the reports, no matter how passionately they are asserted. |
| 17077 | The height of a flagpole could be fixed by its angle of shadow, but that would be very unusual [Smart] |
| Full Idea: You could imagine a person using the angle from a theodolite to decide a suitable spot to cut the height of the flagpole, …but since such circumstances would be very unusual we naturally say the flagpole subtends the angle because of its height. | |
| From: J.J.C. Smart (Explanation - Opening Address [1990], p.14) | |
| A reaction: [compressed; he mentions Van Fraassen 1980:132-3 for a similar point] As a response this seems a bit lame, if the direction is fixed by what is 'usual'. I think the key point is that the direction of explanation is one way or the other, not both. |
| 17078 | Universe expansion explains the red shift, but not vice versa [Smart] |
| Full Idea: The theory of the expansion of the universe renders the red shift no longer puzzling, whereas he expansion of the universe is hardly rendered less puzzling by facts about the red shift. | |
| From: J.J.C. Smart (Explanation - Opening Address [1990], p.15) | |
| A reaction: The direction of explanation is, I take it, made obvious by the direction of causation, with questions about what is 'puzzling' as mere side-effects. |
| 17061 | Explanation of a fact is fitting it into a system of beliefs [Smart] |
| Full Idea: I want to characterise explanation of some fact as a matter of fitting belief in this fact into a system of beliefs. | |
| From: J.J.C. Smart (Explanation - Opening Address [1990], p.02) | |
| A reaction: Sounds good to me. Simple facts slot straight into daily beliefs, and deep obscure facts are explained when we hook them up to things we have already grasped. Quark theory fits into prior physics of forces, properties etc. |
| 17074 | Explanations are bad by fitting badly with a web of beliefs, or fitting well into a bad web [Smart] |
| Full Idea: An explanation may be bad if it fits only into a bad web of belief. It can also be bad if it fits into a (possibly good) web of belief in a bad sort of way. | |
| From: J.J.C. Smart (Explanation - Opening Address [1990], p.09) | |
| A reaction: Nice. If you think someone has an absurd web of beliefs, then it counts against some belief (for you) if it fits beautifully into the other person's belief system. Judgement of coherence comes in at different levels. |
| 17076 | Deducing from laws is one possible way to achieve a coherent explanation [Smart] |
| Full Idea: The Hempelian deductive-nomological model of explanation clearly fits in well with the notion of explanation in terms of coherence. One way of fitting a belief into a system is to show that it is deducible from other beliefs. | |
| From: J.J.C. Smart (Explanation - Opening Address [1990], p.13) | |
| A reaction: Smart goes on to reject the law-based deductive approach, for familiar reasons, but at least it has something in common with the Smart view of explanation, which is the one I like. |
| 17071 | An explanation is better if it also explains phenomena from a different field [Smart] |
| Full Idea: One explanation will be a better explanation that another if it also explains a set of phenomena from a different field ('consilience'). | |
| From: J.J.C. Smart (Explanation - Opening Address [1990], p.07) | |
| A reaction: This would count as 'unexpected accommodation', rather than prediction. It is a nice addition to Lipton's comparison of mere accommodation versus prediction as criteria. It sounds like a strong criterion for a persuasive explanation. |
| 17062 | If scientific explanation is causal, that rules out mathematical explanation [Smart] |
| Full Idea: I class mathematical explanation with scientific explanation. This would be resisted by those who, unlike me, regard the notion of causation as essential to scientific explanation. | |
| From: J.J.C. Smart (Explanation - Opening Address [1990], p.02-3) | |
| A reaction: I aim to champion mathematical explanation, in terms of axioms etc., so I am realising that my instinctive attraction to exclusively causal explanation won't do. What explanation needs is a direction of dependence. |
| 17075 | Scientific explanation tends to reduce things to the unfamiliar (not the familiar) [Smart] |
| Full Idea: The history of science suggests that most often explanation is reduction to the unfamiliar. | |
| From: J.J.C. Smart (Explanation - Opening Address [1990], p.11) | |
| A reaction: Boyle was keen to reduce things to the familiar, but that was early days for science, and some nasty shocks were coming our way. What would Boyle make of quantum non-locality? |
| 22405 | Negative utilitarianism implies that the world should be destroyed, to avoid future misery [Smart] |
| Full Idea: The doctrine of negative utilitarianism (that we should concern ourselves with the minimisation of suffering, rather than the maximisation of happiness) ...means we should support a tyrant who explodes the world, to prevent infinite future misery. | |
| From: J.J.C. Smart (Outline of a System of Utilitarianism [1973], 5) | |
| A reaction: That only seems to imply that the negative utilitarian rule needs supplementary rules. We are too fond of looking for one single moral rule that guides everything. |
| 22404 | Any group interested in ethics must surely have a sentiment of generalised benevolence [Smart] |
| Full Idea: A utilitarian can appeal to the sentiment of generalised benevolence, which is surely present in any group with whom it is profitable to discuss ethical questions. | |
| From: J.J.C. Smart (Outline of a System of Utilitarianism [1973], I) | |
| A reaction: But ethics is not intended only for those who are interested in ethics. If this is the basics of ethics, then we must leave the mafia to pursue its sordid activities without criticism. Their lack of sympathy seems to be their good fortune. |
| 6005 | Animals are dangerous and nourishing, and can't form contracts of justice [Hermarchus, by Sedley] |
| Full Idea: Hermarchus said that animal killing is justified by considerations of human safety and nourishment and by animals' inability to form contractual relations of justice with us. | |
| From: report of Hermarchus (fragments/reports [c.270 BCE]) by David A. Sedley - Hermarchus | |
| A reaction: Could the last argument be used to justify torturing animals? Or could we eat a human who was too brain-damaged to form contracts? |
| 14613 | Special relativity won't determine a preferred frame, but we can pick one externally [Smart] |
| Full Idea: Though special relativity does not determine a preferred frame of reference, it does not rule out the possibility of a frame being determined from outside the theory. Perhaps we should prefer a frame where background radiation is equal in all directions. | |
| From: J.J.C. Smart (The Tenseless Theory of Time [2008], 3) | |
| A reaction: Of course this is a mere philosopher offering the escape clause, and not some Nobel-winning physicist, but I start from the assumption that this idea is plausible, and I am unmoved by the contempt for presentism among relativity geeks. |
| 17063 | Unlike Newton, Einstein's general theory explains the perihelion of Mercury [Smart] |
| Full Idea: Newtonian celestial mechanics does not explain the advance of the perihelion of Mercury, while Einstein's general theory of relativity does. | |
| From: J.J.C. Smart (Explanation - Opening Address [1990], p.03) | |
| A reaction: A perfect example of why explanation is the central concept in science, and probably in all epistemological activity. The desire to know is the desire for an explanation. Once the explanation is obvious, we know. |
| 14615 | If time flows, then 'how fast does it flow?' is a tricky question [Smart] |
| Full Idea: If it is said that time flows, then it seems that the question 'how fast does it flow?' is a devastating one for the A-theorist. | |
| From: J.J.C. Smart (The Tenseless Theory of Time [2008], 5) | |
| A reaction: This is one of the basic landmarks in any debate on time. Time can't be understood by analogy with anything else (such as a river) it seems. |
| 14614 | The past, present, future and tenses of A-theory are too weird, and should be analysed indexically [Smart] |
| Full Idea: The main objections to the A-theory are due to the metaphysical mysteriousness of the A-theory ideas of past, present and future, and also tenses, and to the greater plausibility of analyzing them as indexicals. | |
| From: J.J.C. Smart (The Tenseless Theory of Time [2008], 3) | |
| A reaction: When it comes to time, every theory that has ever been though of is deeply weird, so the basic objection doesn't bother me. Analysing as indexicals just seems to be a technical way of denying reality to the present. |