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. |
| 14255 | We understand things through their dependency relations [Fine,K] |
| Full Idea: We understand a defined object (what it is) through the objects on which it depends. | |
| From: Kit Fine (Ontological Dependence [1995], II) | |
| A reaction: This places dependency relations right at the heart of our understanding of the world, and hence shifts traditional metaphysics away from existence and identity. The notion of explanation is missing from Fine's account. |
| 14250 | Metaphysics deals with the existence of things and with the nature of things [Fine,K] |
| Full Idea: Metaphysics has two main areas of concern: one is with the nature of things, with what they are; and the other is with the existence of things, with whether they are. | |
| From: Kit Fine (Ontological Dependence [1995], I) | |
| A reaction: This paper is part of a movement which has shifted metaphysics to a third target - how things relate to one another. The possibility that this third aim should be the main one seems quite plausible to me. |
| 14259 | Maybe two objects might require simultaneous real definitions, as with two simultaneous terms [Fine,K] |
| Full Idea: In Wooster as the witless bachelor and Jeeves as the crafty manservant, and one valet to the other, we will have the counterpart, within the framework of real definition, to the simultaneous definition of two terms. | |
| From: Kit Fine (Ontological Dependence [1995], III) | |
| A reaction: This is wonderful grist to the mill of scientific essentialism, which endeavours to produce an understanding through explanation of the complex interactions of nature. |
| 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? |
| 14253 | An object's 'being' isn't existence; there's more to an object than existence, and its nature doesn't include existence [Fine,K] |
| Full Idea: It seems wrong to identify the 'being' of an object, its being what it is, with its existence. In one respect existence is too weak; for there is more to an object than mere existence; also too strong, for an object's nature need not include existence. | |
| From: Kit Fine (Ontological Dependence [1995], I) | |
| A reaction: The word 'being' has been shockingly woolly, from Parmenides to Heidegger, but if you identify it with a thing's 'nature' that strikes me as much clearer (even if a little misty). |
| 14261 | There is 'weak' dependence in one definition, and 'strong' dependence in all the definitions [Fine,K] |
| Full Idea: An object 'weakly' depends upon another if it is ineliminably involved in one of its definitions; and it 'strongly' depends upon the other if it is ineliminably involved in all of its definitions. | |
| From: Kit Fine (Ontological Dependence [1995], III) | |
| A reaction: It is important to remember that a definition can be very long, and not just what might go into a dictionary. |
| 14251 | A natural modal account of dependence says x depends on y if y must exist when x does [Fine,K] |
| Full Idea: A natural account of dependence in terms of modality and existence is that one thing x will depend on another thing y just in case it is necessary that y exists if x exists (or in the symbolism of modal logic, □(Ex→Ey). | |
| From: Kit Fine (Ontological Dependence [1995], I) | |
| A reaction: He is going to criticise this view (which he traces back to Aristotle and Husserl). It immediately seems possible that there might be counterexamples. x might depend on y, but not necessarily depend on y. Necessities may not produce dependence. |
| 14257 | An object depends on another if the second cannot be eliminated from the first's definition [Fine,K] |
| Full Idea: The objects upon which a given object depends, according to the present account, are those which must figure in any of the logically equivalent definitions of the object. They will, in a sense, be ineliminable. | |
| From: Kit Fine (Ontological Dependence [1995], II) | |
| A reaction: This is Fine's main proposal for the dependency relationship, with a context of Aristotelian essences understood as definitions. Sounds pretty good to me. |
| 14254 | Dependency is the real counterpart of one term defining another [Fine,K] |
| Full Idea: The notion of one object depending upon another is the real counterpart to the nominal notion of one term being definable in terms of another. | |
| From: Kit Fine (Ontological Dependence [1995], II) | |
| A reaction: This begins to fill out the Aristotelian picture very nicely, since definitions are right at the centre of the nature of things (though a much more transitional part of the story than Fine seems to think). |
| 14252 | We should understand identity in terms of the propositions it renders true [Fine,K] |
| Full Idea: We should understand the identity or being of an object in terms of the propositions rendered true by its identity rather than the other way round. | |
| From: Kit Fine (Ontological Dependence [1995], I) | |
| A reaction: Behind this is an essentialist view of identity, rather than one connected with necessary properties. |
| 14256 | How do we distinguish basic from derived esssences? [Fine,K] |
| Full Idea: How and where are we to draw the line between what is basic to the essence and what is derived? | |
| From: Kit Fine (Ontological Dependence [1995], II) | |
| A reaction: He calls the basic essence 'constitutive' and the rest the 'consequential' essence. This question is obviously very challenging for the essentialist. See Idea 22. |
| 14258 | Maybe some things have essential relationships as well as essential properties [Fine,K] |
| Full Idea: It is natural to suppose, in the case of such objects as Wooster and Jeeves, that in addition to possessing constitutive essential properties they will also enter into constitutive essential relationships. | |
| From: Kit Fine (Ontological Dependence [1995], III) | |
| A reaction: I like this. If we are going to have scientific essences as structures of intrinsic powers, then the relationships between the parts of the essence must also be essential. That is the whole point - that the powers dictate the relationships. |
| 14260 | An object only essentially has a property if that property follows from every definition of the object [Fine,K] |
| Full Idea: We can say that an object essentially has a certain property if its having that property follows from every definition of the object, while an object will definitively have a given property if its having that property follows from some definition of it. | |
| From: Kit Fine (Ontological Dependence [1995], III) | |
| A reaction: Presumably that will be every accurate definition. This nicely allows for the fact that at least nominal definitions may not be unique, and there is even room for real definitions not to be fully determinate (thus, how far should they extend?). |
| 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. |
| 7903 | The six perfections are giving, morality, patience, vigour, meditation, and wisdom [Nagarjuna] |
| Full Idea: The six perfections are of giving, morality, patience, vigour, meditation, and wisdom. | |
| From: Nagarjuna (Mahaprajnaparamitashastra [c.120], 88) | |
| A reaction: What is 'morality', if giving is not part of it? I like patience and vigour being two of the virtues, which immediately implies an Aristotelian mean (which is always what is 'appropriate'). |