45 ideas
| 21360 | Unobservant thinkers tend to dogmatise using insufficient facts [Aristotle] |
| Full Idea: Those whom devotion to abstract discussions has rendered unobservant of the facts are too ready to dogmatise on the basis of a few observations. | |
| From: Aristotle (Coming-to-be and Passing-away (Gen/Corr) [c.335 BCE], 316a09) | |
| A reaction: I totally approve of the idea that a good philosopher should be 'observant'. Prestige in modern analytic philosophy comes from logical ability. There should be some rival criterion for attentiveness to facts, with equal prestige. |
| 21752 | Prior to Gödel we thought truth in mathematics consisted in provability [Gödel, by Quine] |
| Full Idea: Gödel's proof wrought an abrupt turn in the philosophy of mathematics. We had supposed that truth, in mathematics, consisted in provability. | |
| From: report of Kurt Gödel (On Formally Undecidable Propositions [1931]) by Willard Quine - Forward to Gödel's Unpublished | |
| A reaction: This explains the crisis in the early 1930s, which Tarski's theory appeared to solve. |
| 17835 | Gödel show that the incompleteness of set theory was a necessity [Gödel, by Hallett,M] |
| Full Idea: Gödel's incompleteness results of 1931 show that all axiom systems precise enough to satisfy Hilbert's conception are necessarily incomplete. | |
| From: report of Kurt Gödel (On Formally Undecidable Propositions [1931]) by Michael Hallett - Introduction to Zermelo's 1930 paper p.1215 | |
| A reaction: [Hallett italicises 'necessarily'] Hilbert axioms have to be recursive - that is, everything in the system must track back to them. |
| 17886 | The limitations of axiomatisation were revealed by the incompleteness theorems [Gödel, by Koellner] |
| Full Idea: The inherent limitations of the axiomatic method were first brought to light by the incompleteness theorems. | |
| From: report of Kurt Gödel (On Formally Undecidable Propositions [1931]) by Peter Koellner - On the Question of Absolute Undecidability 1.1 |
| 10071 | Second Incompleteness: nice theories can't prove their own consistency [Gödel, by Smith,P] |
| Full Idea: Second Incompleteness Theorem: roughly, nice theories that include enough basic arithmetic can't prove their own consistency. | |
| From: report of Kurt Gödel (On Formally Undecidable Propositions [1931]) by Peter Smith - Intro to Gödel's Theorems 1.5 | |
| A reaction: On the face of it, this sounds less surprising than the First Theorem. Philosophers have often noticed that it seems unlikely that you could use reason to prove reason, as when Descartes just relies on 'clear and distinct ideas'. |
| 19123 | If soundness can't be proved internally, 'reflection principles' can be added to assert soundness [Gödel, by Halbach/Leigh] |
| Full Idea: Gödel showed PA cannot be proved consistent from with PA. But 'reflection principles' can be added, which are axioms partially expressing the soundness of PA, by asserting what is provable. A Global Reflection Principle asserts full soundness. | |
| From: report of Kurt Gödel (On Formally Undecidable Propositions [1931]) by Halbach,V/Leigh,G.E. - Axiomatic Theories of Truth (2013 ver) 1.2 | |
| A reaction: The authors point out that this needs a truth predicate within the language, so disquotational truth won't do, and there is a motivation for an axiomatic theory of truth. |
| 10621 | Gödel's First Theorem sabotages logicism, and the Second sabotages Hilbert's Programme [Smith,P on Gödel] |
| Full Idea: Where Gödel's First Theorem sabotages logicist ambitions, the Second Theorem sabotages Hilbert's Programme. | |
| From: comment on Kurt Gödel (On Formally Undecidable Propositions [1931]) by Peter Smith - Intro to Gödel's Theorems 36 | |
| A reaction: Neo-logicism (Crispin Wright etc.) has a strategy for evading the First Theorem. |
| 17888 | The undecidable sentence can be decided at a 'higher' level in the system [Gödel] |
| Full Idea: My undecidable arithmetical sentence ...is not at all absolutely undecidable; rather, one can always pass to 'higher' systems in which the sentence in question is decidable. | |
| From: Kurt Gödel (On Formally Undecidable Propositions [1931]), quoted by Peter Koellner - On the Question of Absolute Undecidability 1.1 | |
| A reaction: [a 1931 MS] He says the reals are 'higher' than the naturals, and the axioms of set theory are higher still. The addition of a truth predicate is part of what makes the sentence become decidable. |
| 10132 | There can be no single consistent theory from which all mathematical truths can be derived [Gödel, by George/Velleman] |
| Full Idea: Gödel's far-reaching work on the nature of logic and formal systems reveals that there can be no single consistent theory from which all mathematical truths can be derived. | |
| From: report of Kurt Gödel (On Formally Undecidable Propositions [1931]) by A.George / D.J.Velleman - Philosophies of Mathematics Ch.8 |
| 13212 | Infinity is only potential, never actual [Aristotle] |
| Full Idea: Nothing is actually infinite. A thing is infinite only potentially. | |
| From: Aristotle (Coming-to-be and Passing-away (Gen/Corr) [c.335 BCE], 318a21) | |
| A reaction: Aristotle is the famous spokesman for this view, though it reappeared somewhat in early twentieth century discussions (e.g. Hilbert). I sympathise with this unfashionable view. Multiple infinites are good fun, but no one knows what they really are. |
| 3198 | Gödel showed that arithmetic is either incomplete or inconsistent [Gödel, by Rey] |
| Full Idea: Gödel's theorem states that either arithmetic is incomplete, or it is inconsistent. | |
| From: report of Kurt Gödel (On Formally Undecidable Propositions [1931]) by Georges Rey - Contemporary Philosophy of Mind 8.7 |
| 10072 | First Incompleteness: arithmetic must always be incomplete [Gödel, by Smith,P] |
| Full Idea: First Incompleteness Theorem: any properly axiomatised and consistent theory of basic arithmetic must remain incomplete, whatever our efforts to complete it by throwing further axioms into the mix. | |
| From: report of Kurt Gödel (On Formally Undecidable Propositions [1931]) by Peter Smith - Intro to Gödel's Theorems 1.2 | |
| A reaction: This is because it is always possible to formulate a well-formed sentence which is not provable within the theory. |
| 9590 | Arithmetical truth cannot be fully and formally derived from axioms and inference rules [Gödel, by Nagel/Newman] |
| Full Idea: The vast continent of arithmetical truth cannot be brought into systematic order by laying down a fixed set of axioms and rules of inference from which every true mathematical statement can be formally derived. For some this was a shocking revelation. | |
| From: report of Kurt Gödel (On Formally Undecidable Propositions [1931]) by E Nagel / JR Newman - Gödel's Proof VII.C | |
| A reaction: Good news for philosophy, I'd say. The truth cannot be worked out by mechanical procedures, so it needs the subtle and intuitive intelligence of your proper philosopher (Parmenides is the role model) to actually understand reality. |
| 11069 | Gödel's Second says that semantic consequence outruns provability [Gödel, by Hanna] |
| Full Idea: Gödel's Second Incompleteness Theorem says that true unprovable sentences are clearly semantic consequences of the axioms in the sense that they are necessarily true if the axioms are true. So semantic consequence outruns provability. | |
| From: report of Kurt Gödel (On Formally Undecidable Propositions [1931]) by Robert Hanna - Rationality and Logic 5.3 |
| 10118 | First Incompleteness: a decent consistent system is syntactically incomplete [Gödel, by George/Velleman] |
| Full Idea: First Incompleteness Theorem: If S is a sufficiently powerful formal system, then if S is consistent then S is syntactically incomplete. | |
| From: report of Kurt Gödel (On Formally Undecidable Propositions [1931]) by A.George / D.J.Velleman - Philosophies of Mathematics Ch.6 | |
| A reaction: Gödel found a single sentence, effectively saying 'I am unprovable in S', which is neither provable nor refutable in S. |
| 10122 | Second Incompleteness: a decent consistent system can't prove its own consistency [Gödel, by George/Velleman] |
| Full Idea: Second Incompleteness Theorem: If S is a sufficiently powerful formal system, then if S is consistent then S cannot prove its own consistency | |
| From: report of Kurt Gödel (On Formally Undecidable Propositions [1931]) by A.George / D.J.Velleman - Philosophies of Mathematics Ch.6 | |
| A reaction: This seems much less surprising than the First Theorem (though it derives from it). It was always kind of obvious that you couldn't use reason to prove that reason works (see, for example, the Cartesian Circle). |
| 10611 | There is a sentence which a theory can show is true iff it is unprovable [Gödel, by Smith,P] |
| Full Idea: The original Gödel construction gives us a sentence that a theory shows is true if and only if it satisfies the condition of being unprovable-in-that-theory. | |
| From: report of Kurt Gödel (On Formally Undecidable Propositions [1931]) by Peter Smith - Intro to Gödel's Theorems 20.5 |
| 10867 | 'This system can't prove this statement' makes it unprovable either way [Gödel, by Clegg] |
| Full Idea: An approximation of Gödel's Theorem imagines a statement 'This system of mathematics can't prove this statement true'. If the system proves the statement, then it can't prove it. If the statement can't prove the statement, clearly it still can't prove it. | |
| From: report of Kurt Gödel (On Formally Undecidable Propositions [1931]) by Brian Clegg - Infinity: Quest to Think the Unthinkable Ch.15 | |
| A reaction: Gödel's contribution to this simple idea seems to be a demonstration that formal arithmetic is capable of expressing such a statement. |
| 8747 | Realists are happy with impredicative definitions, which describe entities in terms of other existing entities [Gödel, by Shapiro] |
| Full Idea: Gödel defended impredicative definitions on grounds of ontological realism. From that perspective, an impredicative definition is a description of an existing entity with reference to other existing entities. | |
| From: report of Kurt Gödel (On Formally Undecidable Propositions [1931]) by Stewart Shapiro - Thinking About Mathematics 5.3 | |
| A reaction: This is why constructivists must be absolutely precise about definition, where realists only have to do their best. Compare building a car with painting a landscape. |
| 13221 | Existence is either potential or actual [Aristotle] |
| Full Idea: Some things are-potentially while others are-actually. | |
| From: Aristotle (Coming-to-be and Passing-away (Gen/Corr) [c.335 BCE], 327b24) | |
| A reaction: I've read a lot of Aristotle, but am still not quite clear what this distinction means. I like the distinction between a thing's actual being and its 'modal profile', but the latter may extend well beyond what Aristotle means by potential being. |
| 16100 | True change is in a thing's logos or its matter, not in its qualities [Aristotle] |
| Full Idea: In that which underlies a change there is a factor corresponding to the definition [logon] and there is a material factor. When a change is in these constitutive factors there is coming to be or passing away, but in a thing's qualities it is alteration. | |
| From: Aristotle (Coming-to-be and Passing-away (Gen/Corr) [c.335 BCE], 317a24) | |
| A reaction: This seems to be a key summary of Aristotle's account of change, in the context of his hylomorphism (form-plus-matter). The logos is the account of the thing, which seems to be the definition, which seems to give the form (principle or structure). |
| 16101 | A change in qualities is mere alteration, not true change [Aristotle] |
| Full Idea: When a change occurs in the qualities [pathesi] and is accidental [sumbebekos], there is alteration (rather than true change). | |
| From: Aristotle (Coming-to-be and Passing-away (Gen/Corr) [c.335 BCE], 317a27) | |
| A reaction: [tr. partly Gill] Aristotle doesn't seem to have a notion of 'properties' in quite our sense. 'Pathe' seems to mean experienced qualities, rather than genuine causal powers. Gill says 'pathe' are always accidental. |
| 12133 | If the substratum persists, it is 'alteration'; if it doesn't, it is 'coming-to-be' or 'passing-away' [Aristotle] |
| Full Idea: Since we must distinguish the substratum and the property whose nature is to be predicated of the substratum,..there is alteration when the substratum persists...but when nothing perceptible persists as a substratum, this is coming-to-be and passing-away. | |
| From: Aristotle (Coming-to-be and Passing-away (Gen/Corr) [c.335 BCE], 319b08-16) | |
| A reaction: As usual, Aristotle clarifies the basis of the problem, by distinguishing two different types of change. Notice the empirical character of his approach, resting on whether or not the substratum is 'perceptible'. |
| 13213 | All comings-to-be are passings-away, and vice versa [Aristotle] |
| Full Idea: Every coming-to-be is a passing away of something else and every passing-away some other thing's coming-to-be. | |
| From: Aristotle (Coming-to-be and Passing-away (Gen/Corr) [c.335 BCE], 319a07) | |
| A reaction: This seems to be the closest that Aristotle gets to sympathy with the Heraclitus view that all is flux. When a sparrow dies and disappears, I am not at all clear what comes to be, except some ex-sparrow material. |
| 12134 | Matter is the substratum, which supports both coming-to-be and alteration [Aristotle] |
| Full Idea: Matter, in the proper sense of the term, is to be identified with the substratum which is receptive of coming-to-be and passing-away; but the substratum of the remaining kinds of change is also matter, because these substrata receive contraries. | |
| From: Aristotle (Coming-to-be and Passing-away (Gen/Corr) [c.335 BCE], 320a03) | |
| A reaction: This must be compared with his complex discussion of the role of matter in his Metaphysics, where he has introduced 'form' as the essence of things. I don't think the two texts are inconsistent, but it's tricky... See Idea 12133 on types of change. |
| 16572 | Does the pure 'this' come to be, or the 'this-such', or 'so-great', or 'somewhere'? [Aristotle] |
| Full Idea: The question might be raised whether substance (i.e. the 'this') comes-to-be at all. Is it not rather the 'such', the 'so-great', or the 'somewhere', which comes-to-be? | |
| From: Aristotle (Coming-to-be and Passing-away (Gen/Corr) [c.335 BCE], 317b21) | |
| A reaction: This is interesting because it pulls the 'tode ti', the 'this-such', apart, showing that he does have a concept of a pure 'this', which seems to constitute the basis of being ('ousia'). We can say 'this thing', or 'one of these things'. |
| 16573 | Philosophers have worried about coming-to-be from nothing pre-existing [Aristotle] |
| Full Idea: In addition, coming-to-be may proceed out of nothing pre-existing - a thesis which, more than any other, preoccupied and alarmed the earliest philosophers. | |
| From: Aristotle (Coming-to-be and Passing-away (Gen/Corr) [c.335 BCE], 317b29) | |
| A reaction: This is the origin of the worry about 'ex nihilo' coming-to-be. Christians tended to say that only God could create in this way. |
| 13214 | The substratum changing to a contrary is the material cause of coming-to-be [Aristotle] |
| Full Idea: The substratum [hupokeimenon?] is the material cause of the continuous occurrence of coming-to-be, because it is such as to change from contrary to contrary. | |
| From: Aristotle (Coming-to-be and Passing-away (Gen/Corr) [c.335 BCE], 319a19) | |
| A reaction: Presumably Aristotle will also be seeking the 'formal' cause as well as the 'material' cause (not to mention the 'efficient' and 'final' causes). |
| 13215 | If a perceptible substratum persists, it is 'alteration'; coming-to-be is a complete change [Aristotle] |
| Full Idea: There is 'alteration' when the substratum is perceptible and persists, but changes in its own properties. ...But when nothing perceptible persists in its identity as a substratum, and the thing changes as a whole, it is coming-to-be of a substance. | |
| From: Aristotle (Coming-to-be and Passing-away (Gen/Corr) [c.335 BCE], 319b11-17) | |
| A reaction: [compressed] Note that a substratum can be perceptible - it isn't just some hidden mystical I-know-not-what (as Locke calls it). This whole text is a wonderful source on the subject of physical change. Note too the reliance on what is perceptible. |
| 16717 | Which of the contrary features of a body are basic to it? [Aristotle] |
| Full Idea: What sorts of contrarities, and how many of them, are to be accounted 'originative sources' of body? | |
| From: Aristotle (Coming-to-be and Passing-away (Gen/Corr) [c.335 BCE], 329b04) | |
| A reaction: Pasnau says these pages of Aristotle are the source of the doctrine of primary and secondary qualities. Essentially, hot, cold, wet and dry are his four primary qualities. |
| 3192 | Basic logic can be done by syntax, with no semantics [Gödel, by Rey] |
| Full Idea: Gödel in his completeness theorem for first-order logic showed that a certain set of syntactically specifiable rules was adequate to capture all first-order valid arguments. No semantics (e.g. reference, truth, validity) was necessary. | |
| From: report of Kurt Gödel (On Formally Undecidable Propositions [1931]) by Georges Rey - Contemporary Philosophy of Mind 8.2 | |
| A reaction: This implies that a logic machine is possible, but we shouldn't raise our hopes for proper rationality. Validity can be shown for purely algebraic arguments, but rationality requires truth as well as validity, and that needs propositions and semantics. |
| 1748 | Archelaus was the first person to say that the universe is boundless [Archelaus, by Diog. Laertius] |
| Full Idea: Archelaus was the first person to say that the universe is boundless. | |
| From: report of Archelaus (fragments/reports [c.450 BCE]) by Diogenes Laertius - Lives of Eminent Philosophers 02.Ar.3 |
| 13216 | Matter is the limit of points and lines, and must always have quality and form [Aristotle] |
| Full Idea: The matter is that of which points and lines are limits, and it is something that can never exist without quality and without form. | |
| From: Aristotle (Coming-to-be and Passing-away (Gen/Corr) [c.335 BCE], 320b16) | |
| A reaction: There seems to be a contradiction here somewhere. Matter has to be substantial enough to have a form, and yet seems to be the collective 'limit' of the points and lines. I wonder what 'limit' is translating? Sounds a bit too modern. |
| 17994 | The primary matter is the substratum for the contraries like hot and cold [Aristotle] |
| Full Idea: We must reckon as an 'orginal source' and as 'primary' the matter which underlies, though it is inseparable from the contrary qualities: for 'the hot' is not matter for 'the cold' nor 'cold' for 'hot', but the substratum is matter for them both. | |
| From: Aristotle (Coming-to-be and Passing-away (Gen/Corr) [c.335 BCE], 329a30) | |
| A reaction: A much discussed passage. |
| 13224 | There couldn't be just one element, which was both water and air at the same time [Aristotle] |
| Full Idea: No one supposes a single 'element' to persist, as the basis of all, in such a way that it is Water as well as Air (or any other element) at the same time. | |
| From: Aristotle (Coming-to-be and Passing-away (Gen/Corr) [c.335 BCE], 332a09) | |
| A reaction: Of course, we now think that oxygen is a key part of both water and of air, but Aristotle's basic argument still seems right. How could multiplicity be explained by a simply unity? The One is cool, but explains nothing. |
| 16594 | The Four Elements must change into one another, or else alteration is impossible [Aristotle] |
| Full Idea: These bodies (Fire, Water and the like) change into one another (and are not immutable as Empedocles and other thinkers assert, since 'alteration' would then have been impossible). | |
| From: Aristotle (Coming-to-be and Passing-away (Gen/Corr) [c.335 BCE], 329b1) | |
| A reaction: This is why Aristotle proposes that matter [hule] underlies the four elements. Gill argues that by matter Aristotle means the elements. |
| 13223 | Fire is hot and dry; Air is hot and moist; Water is cold and moist; Earth is cold and dry [Aristotle] |
| Full Idea: The four couples of elementary qualities attach themselves to the apparently 'simple' bodies (Fire, Air, Earth, Water). Fire is hot and dry, whereas Air is hot and moist (being a sort of aqueous vapour); Water is cold and moist, and Earth is cold and dry. | |
| From: Aristotle (Coming-to-be and Passing-away (Gen/Corr) [c.335 BCE], 330b02) | |
| A reaction: This is the traditional framework accepted throughout the middle ages, and which had a huge influence on medicine. It all looks rather implausible now. Aristotle was a genius, but not critical enough about evidence. |
| 13220 | Bodies are endlessly divisible [Aristotle] |
| Full Idea: Bodies are divisible through and through. | |
| From: Aristotle (Coming-to-be and Passing-away (Gen/Corr) [c.335 BCE], 326b27) | |
| A reaction: This is Aristotle's flat rejection of atomism, arrived at after several sustained discussions, in this text and elsewhere. I don't think we are in a position to say that Aristotle is wrong. |
| 13210 | Wood is potentially divided through and through, so what is there in the wood besides the division? [Aristotle] |
| Full Idea: If having divided a piece of wood I put it together, it is equal to what it was and is one. This is so whatever the point at which I cut the wood. The wood is therefore divided potentially through and through. So what is in the wood besides the division? | |
| From: Aristotle (Coming-to-be and Passing-away (Gen/Corr) [c.335 BCE], 316b11) | |
| A reaction: Part of a very nice discussion of the implications of the thought experiment of cutting something 'through and through'. It seems to me that the arguments are still relevant, in the age of quarks, electrons and strings. |
| 13211 | If a body is endlessly divided, is it reduced to nothing - then reassembled from nothing? [Aristotle] |
| Full Idea: Dividing a body at all points might actually occur, so the body will be both actually indivisible and potentially divided. Then nothing will remain and the body passes into what is incorporeal. So it might be reassembled out of points, or out of nothing. | |
| From: Aristotle (Coming-to-be and Passing-away (Gen/Corr) [c.335 BCE], 316b24) | |
| A reaction: [a bit compressed] This sounds like an argument in favour of atomism, but Aristotle was opposed to that view. He is aware of the contradictions that seem to emerge with infinite division. Graham Priest is interesting on the topic. |
| 13228 | There is no time without movement [Aristotle] |
| Full Idea: There can be no time without movement. | |
| From: Aristotle (Coming-to-be and Passing-away (Gen/Corr) [c.335 BCE], 337a24) | |
| A reaction: See Shoemaker's nice thought experiment as a challenge to this. Intuition seems to cry out that if movement stopped for a moment, that would not stop time, even though there was no way to measure its passing. |
| 16595 | If each thing can cease to be, why hasn't absolutely everything ceased to be long ago? [Aristotle] |
| Full Idea: If some one of the things 'which are' is constantly disappearing, why has not the whole of 'what is' been used up long ago and vanished away - assuming of course that the material of all the several comings-to-be was infinite? | |
| From: Aristotle (Coming-to-be and Passing-away (Gen/Corr) [c.335 BCE], 318a17) | |
| A reaction: This thought is the basis of Aquinas's Third Way for proving the existence of God (as the force which prevents the vicissitudes of nature from sliding into oblivion). |
| 5989 | Archelaus said life began in a primeval slime [Archelaus, by Schofield] |
| Full Idea: Archelaus wrote that life on Earth began in a primeval slime. | |
| From: report of Archelaus (fragments/reports [c.450 BCE]) by Malcolm Schofield - Archelaus | |
| A reaction: This sounds like a fairly clearcut assertion of the production of life by evolution. Darwin's contribution was to propose the mechanism for achieving it. We should honour the name of Archelaus for this idea. |
| 13227 | Being is better than not-being [Aristotle] |
| Full Idea: Being is better than not-being. | |
| From: Aristotle (Coming-to-be and Passing-away (Gen/Corr) [c.335 BCE], 336b29) | |
| A reaction: [see also Metaphysics 1017a07 ff, says the note] This peculiar assumption is at the heart of the ontological argument. Is the existence of the plague bacterium, or of Satan, or of mass-murderers, superior? |
| 13226 | An Order controls all things [Aristotle] |
| Full Idea: There is an Order controlling all things. | |
| From: Aristotle (Coming-to-be and Passing-away (Gen/Corr) [c.335 BCE], 336b13) | |
| A reaction: Presumably the translator provides the capital letter. How do we get from 'there is an order in all things' to 'there is an order which controls all things'? |