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? |
| 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. |
| 5845 | Niceratus learnt the whole of Homer by heart, as a guide to goodness [Xenophon] |
| Full Idea: Niceratus said that his father, because he was concerned to make him a good man, made him learn the whole works of Homer, and he could still repeat by heart the entire 'Iliad' and 'Odyssey'. | |
| From: Xenophon (Symposium [c.391 BCE], 3.5) | |
| A reaction: This clearly shows the status which Homer had in the teaching of morality in the time of Socrates, and it is precisely this acceptance of authority which he was challenging, in his attempts to analyse the true basis of virtue |
| 23418 | Liberal state legitimacy is based on a belief in justice, not in some conception of the good life [Kymlicka] |
| Full Idea: For liberals the basis of state legitimacy is a shared sense of justice, not a shared conception of the good. | |
| From: Will Kymlicka (Community [1993], 'legitimacy') | |
| A reaction: For a liberal state to work, the citizens have to roughly believe in the core values of liberalism, which are primarily freedom and equality (and hence justice). |
| 23414 | Liberals say state intervention in culture restricts people's autonomy [Kymlicka] |
| Full Idea: According to liberal theory, a state which intervenes in the cultural market place to encourage any particular way of life restricts people's autonomy. | |
| From: Will Kymlicka (Community [1993], 'social') | |
| A reaction: The communitarian idea is that the state should intervene, in order to foster the best aspects of communal culture. The dangers are obvious, and can be seen in any totalitarian state. A gentle hand on the tiller, perhaps? Increase the options? |
| 23410 | Modern liberals see a community as simply a society which respects freedom and equality [Kymlicka] |
| Full Idea: Most contemporary liberal philosophers have little to say about the ideal of community. …It is often seen as derivative of liberty and equality - a society lives up to the ideal of community if its members are treated as free and equal persons. | |
| From: Will Kymlicka (Community [1993], 'Intro') | |
| A reaction: He cites Rawls as an example. This is the central idea which was attacked by modern communitarians. A collection of scattered self-seeking isolated individuals doesn't seem to amount to a healthy communal life. Maybe community needs further rights? |
| 23409 | Community can focus on class or citizenship or ethnicity or culture [Kymlicka] |
| Full Idea: In recent centuries the ideal of community has taken many forms, from class solidarity or shared citizenship to a common ethnic descent or cultural identity. | |
| From: Will Kymlicka (Community [1993], 'Intro') | |
| A reaction: Language and religion are not explicitly mentioned, but must be implied. Supporting a major sports team is also worth mentioning. |
| 23419 | Communitarianism struggles with excluded marginalised groups [Kymlicka] |
| Full Idea: The problem of the exclusion of historically marginalised groups is endemic to the communitarian project. | |
| From: Will Kymlicka (Community [1993], 'legitimacy') | |
| A reaction: Put simply, old-fashioned styles of community are probably impossible in large modern states, some with rather arbitrary borders. |
| 23413 | Feminism has shown that social roles are far from fixed (as communitarians tend to see them) [Kymlicka] |
| Full Idea: Communitarians say that some of our social roles must be regarded as fixed when planning our lives, …but the women's movement has shown how deeply entrenched social roles can be questioned and rejected. | |
| From: Will Kymlicka (Community [1993], 'Embedded') | |
| A reaction: True, but parents walking out on young children also shows that. The ideal must be some sort of balance. |
| 23415 | Participation aids the quest for the good life, but why should that be a state activity? [Kymlicka] |
| Full Idea: Communitarians rarely distinguish between collective activities and political activities. Shared participation aids intelligent decisions about the good life, but why should that be organised through the state, rather than by free individuals? | |
| From: Will Kymlicka (Community [1993], 'need') | |
| A reaction: Kylicka points out later that local groups can be very unintelligent or prejudiced. Modern media have changed that picture, because participation can be with geographically remote people. |
| 23411 | Communitarians see justice as primarily a community matter, rather than a principle [Kymlicka] |
| Full Idea: Communitarians believe either that community replaces the need for principles of justice, or that the community is either the source of such principles or should play a greater role in deciding their content. | |
| From: Will Kymlicka (Community [1993], 'Intro') | |
| A reaction: [compressed] The idea that a racist or chauvinist or puritanical or insular community should decide justice for all its members sounds horrible. It drives you to liberal individualism, just thinking about it. |
| 23412 | Justice resolves conflicts, but may also provoke them [Kymlicka] |
| Full Idea: Justice can help mediate conflicts, but it also tends to creat conflicts, and to decrease the natural expression of sociability. | |
| From: Will Kymlicka (Community [1993], 'limits') | |
| A reaction: [He is discussing Michael Sandel on liberalism] Family life might not go well if all of its members continually demanded justice for themselves as individuals. Maybe our concept of justice is too individualistic? Do we need a sense of 'group' justice? |