23 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? |
| 12887 | A whole must have one characteristic, an internal relation, and a structure [Rescher/Oppenheim] |
| Full Idea: A whole must possess an attribute peculiar to and characteristic of it as a whole; there must be a characteristic relation of dependence between the parts; and the whole must have some structure which gives it characteristics. | |
| From: Rescher,N/Oppenheim,P (Logical Analysis of Gestalt Concepts [1955], p.90), quoted by Peter Simons - Parts 9.2 | |
| A reaction: Simons says these are basically sensible conditions, and tries to fill them out. They seem a pretty good start, and I must resist the temptation to rush to borderline cases. |
| 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. |
| 23429 | The environment needs localised politics, with its care for the land [Dobson] |
| Full Idea: More localised politics helps to generate the disposition of care for the land which is a core feature of environmental politics. | |
| From: Andrew Dobson (Environmental Politics: very short intro [2016], 4) | |
| A reaction: I currently live in a time when localised politics is hugely devalued, because centralisation and privatisation are cheaper. It seems obvious that many human needs require a commitment to a particular locality. |
| 23424 | An ideology judges things now, and offers an ideal, with a strategy for reaching it [Dobson] |
| Full Idea: An ideology generally has three components: a judgement (usually critical) of how things are, a picture of the ideology's ideal society, and a strategy for progressing towards the ideal. | |
| From: Andrew Dobson (Environmental Politics: very short intro [2016], 2) | |
| A reaction: Conservatives tend to think we are already living in the ideal, and they reject most ideologies for being 'idealistic' (which presumably means delusional). I'm a fan of ideals, but combined with cool judgement. |
| 23426 | Ecologism is often non-liberal, by claiming to know other people's best interests [Dobson] |
| Full Idea: Liberals say that their preferences are their interests, and resist the idea that anyone could know their interests better than they can. …To this degree, ecologism might be regarded as 'non-liberal'. | |
| From: Andrew Dobson (Environmental Politics: very short intro [2016], 2) | |
| A reaction: There are lots of other cases where liberal citizens may not realise their best interests, such as in the control of traffic, or of drugs. |
| 23427 | Socialism can be productive and centralised, or less productive and decentralised [Dobson] |
| Full Idea: Marx and his heirs promote a productivist socialism, but utopian socialists such as William Morris offer a less productivist and more decentralised form of socialism. | |
| From: Andrew Dobson (Environmental Politics: very short intro [2016], 2) | |
| A reaction: Modern history teaches us to be very cautious about the centralised version. Presumably you could be decentralised but still value production highly, even if it is a bit less efficient. |
| 23428 | Difference feminists say women differ fundamentally from men [Dobson] |
| Full Idea: Difference feminists argue that men and women are fundamentally different. | |
| From: Andrew Dobson (Environmental Politics: very short intro [2016], 2) | |
| A reaction: You can be significantly different without being 'fundamentally' different. Personally I don't see a huge difference, even though history may have greatly exaggerated and dramatised what differences there are. |
| 23422 | For the environment, affluence and technology matter as much as population size [Dobson] |
| Full Idea: Although bare population figures are important for environmental impact, the level of affluence and the technology are also crucial factors. | |
| From: Andrew Dobson (Environmental Politics: very short intro [2016], 2) | |
| A reaction: It is worth noting that the technology can also have a good impact, though affluence is nearly always bad. |
| 23425 | Ecologism says growth must be reduced, and efficiency is not enough [Dobson] |
| Full Idea: A central belief of the ideology of ecologism is that aggregate growth must be reduced, and that this is very unlikely to be achieved by efficiency gains alone. | |
| From: Andrew Dobson (Environmental Politics: very short intro [2016], 2) | |
| A reaction: He argues that efficiency gains invariably lead to increased production. Trickle down economics needs huge growth to deliver a good life for the poorest sector. Ecologism has to be fairly egalitarian about wealth. |
| 23430 | A million years is a proper unit of political time [Dobson] |
| Full Idea: We must acknowledge that a million years is a proper unit of political time. | |
| From: Andrew Dobson (Environmental Politics: very short intro [2016], 5) | |
| A reaction: [He cites Colin Tudge] Such thinking is almost impossible, but owners of large aristocratic estates seem to have thought in centuries, because they were confident of continuity. The more we identify with all of humanity, the more this is possible. |
| 23423 | We currently value the present fourteen times more highly than the future [Dobson] |
| Full Idea: At current rates we seem to value present concerns as fourteen times more valuable than future concerns. | |
| From: Andrew Dobson (Environmental Politics: very short intro [2016], 2) | |
| A reaction: A sobering figure, which sounds about right. This directly influences how much we spend on future concerns. One thought is that future generations may be much more affluent than us! |