26 ideas
| 8092 | Logic was merely a branch of rhetoric until the scientific 17th century [Devlin] |
| Full Idea: Until the rise of what we call the scientific method in the seventeenth century, logic was regarded largely as one aspect of rhetoric - a study of how one person't argument could convince another. | |
| From: Keith Devlin (Goodbye Descartes [1997], Ch.11) | |
| A reaction: This may well give the main reason why the Greeks invented logic in the first place. Aristotle wrote a book on rhetoric, and that was where the money was. Leibniz is clearly a key figure in the change of attitude. |
| 8081 | 'No councillors are bankers' and 'All bankers are athletes' implies 'Some athletes are not councillors' [Devlin] |
| Full Idea: Most people find it hard to find any conclusion that fits the following premises: 'No councillors are bankers', and 'All bankers are athletes'. There is a valid conclusion ('Some athletes are not councillors') but it takes quite an effort to find it. | |
| From: Keith Devlin (Goodbye Descartes [1997], Ch. 2) | |
| A reaction: A nice illustration of the fact that syllogistic logic is by no means automatic and straightforward. There is a mechanical procedure, but a lot of intuition and common sense is also needed. |
| 8085 | Modern propositional inference replaces Aristotle's 19 syllogisms with modus ponens [Devlin] |
| Full Idea: Where Aristotle had 19 different inference rules (his valid syllogisms), modern propositional logic carries out deductions using just one rule of inference: modus ponens. | |
| From: Keith Devlin (Goodbye Descartes [1997], Ch. 4) | |
| A reaction: At first glance it sounds as if Aristotle's guidelines might be more useful than the modern one, since he tells you something definite and what implies what, where modus ponens just seems to define the word 'implies'. |
| 8086 | Predicate logic retains the axioms of propositional logic [Devlin] |
| Full Idea: Since predicate logic merely extends propositional logic, all the axioms of propositional logic are axioms of predicate logic. | |
| From: Keith Devlin (Goodbye Descartes [1997], Ch. 4) | |
| A reaction: See Idea 7798 for the axioms. |
| 8091 | Situation theory is logic that takes account of context [Devlin] |
| Full Idea: In many respects, situation theory is an extension of classical logic that takes account of context. | |
| From: Keith Devlin (Goodbye Descartes [1997], Ch. 8) | |
| A reaction: John Barwise is cited as the parent of this movement. Many examples show that logical form is very hard to pin down, because word-meaning depends on context (e.g. 'several crumbs' differs from 'several mountains'). |
| 8087 | Golden ages: 1900-1960 for pure logic, and 1950-1985 for applied logic [Devlin] |
| Full Idea: The period from 1900 to about 1960 could be described as the golden age of 'pure' logic, and 1950 to 1985 the golden age of 'applied' logic (e.g. applied to everyday reasoning, and to theories of language). | |
| From: Keith Devlin (Goodbye Descartes [1997], Ch. 4) | |
| A reaction: Why do we always find that we have just missed the Golden Age? However this supports the uneasy feeling that the golden age for all advances in human knowledge is just coming to an end. Biology, including the brain, is the last frontier. |
| 8089 | Montague's intensional logic incorporated the notion of meaning [Devlin] |
| Full Idea: Montague's intensional logic was the first really successful attempt to develop a mathematical framework that incorporates the notion of meaning. | |
| From: Keith Devlin (Goodbye Descartes [1997], Ch. 8) | |
| A reaction: Previous logics, led by Tarski, had flourished by sharply dividing meaning from syntax, and concentrating on the latter. |
| 8082 | Where a conditional is purely formal, an implication implies a link between premise and conclusion [Devlin] |
| Full Idea: Implication involves some form of link or causality between the antecedent and the consequent of an if-then; normally it says that the conclusion is a consequence of the premise (where conditionals are just defined by 'true' and 'false'). | |
| From: Keith Devlin (Goodbye Descartes [1997], Ch. 2) | |
| A reaction: This distinction is a key one when discussing 'If-then' sentences. Some are merely formal conditionals, but others make real claims about where you can get to from where you are. |
| 8072 | Sentences of apparent identical form can have different contextual meanings [Devlin] |
| Full Idea: "Safety goggles must be worn in the building" is clear enough, but "dogs must always be carried on the escalator" doesn't require us to head off in search of a dog. | |
| From: Keith Devlin (Goodbye Descartes [1997], Ch. 1) | |
| A reaction: A nice illustration of how the requirements of logical form will often take us beyond the strict and literal meaning of a sentence, into context, tone, allusion and subjective aspects. |
| 8075 | Space and time are atomic in the arrow, and divisible in the tortoise [Devlin] |
| Full Idea: The arrow paradox starts with the assumption that space and time are atomic; the tortoise starts with the opposite assumption that space and time are infinitely divisible. | |
| From: Keith Devlin (Goodbye Descartes [1997], Ch. 2) | |
| A reaction: Aquinas similarly covers all options (the cosmos has a beginning, or no beginning). The nature of movement in a space which involves quantum leaps remains metaphysically puzzling. Where is a particle at half of the Planck time? |
| 8088 | People still say the Hopi have no time concepts, despite Whorf's later denial [Devlin] |
| Full Idea: The Hopi time myth does not appear to have been stopped for a moment by the fact that Whorf himself subsequently wrote that the Hopi language does indeed have words for past, present, and future | |
| From: Keith Devlin (Goodbye Descartes [1997], Ch. 5) | |
| A reaction: Arguments for relativism based on the Hopi seem now to be thoroughly discredited. Sensible people never believed them in the first place. |
| 8073 | How do we parse 'time flies like an arrow' and 'fruit flies like an apple'? [Devlin] |
| Full Idea: How do people identify subject and verb in the sentences "time flies like an arrow" and "fruit flies like an apple"? | |
| From: Keith Devlin (Goodbye Descartes [1997], Ch. 1) | |
| A reaction: A nice illustration of the fact that even if we have an innate syntax mechanism, it won't work without some semantics, and some experience of the environmental context of utterances. |
| 8076 | The distinction between sentences and abstract propositions is crucial in logic [Devlin] |
| Full Idea: The distinction between sentences and the abstract propositions that they express is one of the key ideas of logic. A logical argument consists of propositions, assembled together in a systematic fashion. | |
| From: Keith Devlin (Goodbye Descartes [1997], Ch. 2) | |
| A reaction: He may claim that arguments consist of abstract propositions, but they always get expressed in sentences. However, the whole idea of logical form implies the existence of propositions - there is something which a messy sentence 'really' says. |
| 23874 | Armies and businesses create moralities in which their activity can do no wrong [Marx, by Weil] |
| Full Idea: Marx saw that social groups manufacture moralities for their own use, so their activity is placed outside the reach of evil. Thus the first articles of soldiers and businessmen is to deny that it is possible to do evil while waging war or doing business. | |
| From: report of Karl Marx (works [1860]) by Simone Weil - Fragments: London 1943 p.146 | |
| A reaction: This is especially true of the modern reverence for 'market forces'. It is a key debate in the ethics of warfare - compare Walzer and McMahon. A striking thought, obviously containing a lot of truth. |
| 18662 | Liberal freedom is the right to be separate, and ignores the union of man with man [Marx] |
| Full Idea: The liberal right of man to freedom is not based on the union of man with man, but on the separation of man from man; it is the right to this separation. | |
| From: Karl Marx (works [1860]), quoted by Will Kymlicka - Contemporary Political Philosophy (1st edn) 7.2.a | |
| A reaction: [quoted from an anthology] It is interesting that liberal freedom is the right NOT to be involved in politics, and even not to vote in elections. Home counties England (high hedges etc) is the embodiment of the freedom not to be involved in society. |
| 23372 | Liberals want the right to be separate, rather than for people to be united [Marx] |
| Full Idea: The [liberal] right of man to freedom is not based on the union of man with man, but on the separation of man from man. It is the right to this separation. | |
| From: Karl Marx (works [1860], p.53), quoted by Will Kymlicka - Contemporary Political Philosophy (2nd edn) 7 | |
| A reaction: [in collection ed.McLelland p.53] That nicely encapsulates the debate. Modern liberal thinkers regret the loss of community, but people in authoritarian communities yearn for separation. You can have too much 'union'! |
| 20576 | Early Marx anticipates communitarian objections to liberalism [Marx, by Oksala] |
| Full Idea: The early writings of Marx anticipate the communitarian critique of liberalism. | |
| From: report of Karl Marx (works [1860]) by Johanna Oksala - Political Philosophy: all that matters Ch.8 | |
| A reaction: [Oksala says modern writers seem to prefer this to the hardcore later Marx, which is presumably too 'scientific'. He says 'Capital Vol 1' is Marx's most important work] |
| 23862 | By saying the material dialectic of history aspires to the best, Marx agreed with capitalism [Weil on Marx] |
| Full Idea: When Marx inverted Hegel's dialectic of history, by substituting matter for mind as the motive, he attributed to matter the essence of mind, an unceasing aspiration towards the best - which was in keeping with the general current of capitalist thought. | |
| From: comment on Karl Marx (works [1860]) by Simone Weil - Reflections on Liberty and Social Oppression p.43 | |
| A reaction: [compressed] A rather nice debating point! Marx seems to share the universal nineteenth century belief in unremitting progress. Without that, it is impossible to believe that a revolution will necessarily improve anything. |
| 21999 | False consciousness results from concealment by the superstructure [Marx, by Singer] |
| Full Idea: False consciousness involves failing to see things as they really are. It comes about because a society's superstructure can conceal the real basis of the society. | |
| From: report of Karl Marx (works [1860]) by Peter Singer - Marx 9 | |
| A reaction: That seems a poor label, probably revealing a Hegelian background. It seems a matter of knowledge rather than consciousness. Can a whole mind be in a state of error? |
| 23875 | Marx says force is everything, and that the weak will become strong, while remaining the weak [Weil on Marx] |
| Full Idea: Marx posits on the one hand that force alone governs social relations to the exclusion of anything else, and on the other hand that one day the weak, while remaining weak, will nevertheless be stronger. He believed in miracles. | |
| From: comment on Karl Marx (works [1860]) by Simone Weil - Fragments: London 1943 p.149 | |
| A reaction: This is close to the obvious contradiction if the working classes despise the middle classes (the dreaded 'bourgeoisie') while their only aspiration is to be like them. It is hard to custom design a new class to which they could both aspire. |
| 18653 | Marx rejected equal rights because they never actually treat people as equals [Marx, by Kymlicka] |
| Full Idea: Marx rejected the idea of equal rights, not because he was not a friend to the idea of treating people as equals, but precisely because he thought rights failed to live up to that ideal. | |
| From: report of Karl Marx (works [1860]) by Will Kymlicka - Contemporary Political Philosophy (1st edn) 5.1 | |
| A reaction: Presumably because the power to award 'rights' goes to the highest bidder. If equality is to be enshrined in law, it is a bit difficult to see how else to manage it. |
| 20958 | Capitalism changes the world, by socialising the idea of a commodity [Marx, by Bowie] |
| Full Idea: In Marx's view the essential factor in capitalism is that the encroachment of the commodity form into society fundamentally changes the world. | |
| From: report of Karl Marx (works [1860]) by Andrew Bowie - Introduction to German Philosophy 6 'Historical' | |
| A reaction: The main point is that people and their labour become commodities. Haven't animals always been treated as commodities? Clearly slave were commodities, long before capitalism. Capitalism universalises it? |
| 23876 | The essence of capitalism is the subordination of people to things [Marx, by Weil] |
| Full Idea: Marx discovered a formula impossible to surpass when he said that the essence of capitalism lies in the subordination of subject to object, of man to thing. | |
| From: report of Karl Marx (works [1860]) by Simone Weil - Fragments: London 1943 p,155 | |
| A reaction: I find this rather too vague to be a penetrating observation. I would suggest the obliteration of cooperation and community, in favour of competition. Winners and losers. |
| 20960 | Marx thought capitalism was partly liberating, and could make labour and ownership more humane [Marx, by Bowie] |
| Full Idea: Marx did not disapprove per se of capitalism. New divisions of labour and forms of ownership could transform individuals in modern societies, creating a more humane world with the means capitalism had liberated from feudalism. | |
| From: report of Karl Marx (works [1860]) by Andrew Bowie - Introduction to German Philosophy 11 'Metaphysics' | |
| A reaction: I'm guessing this might be early Marx, which has less to say about the 'scientific' inevitably of deep change, and the necessity for revolution. Nowadays we tinker with humane changes at the poorer end, while the rich run rampant. |
| 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 |
| 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. |