24 ideas
| 5893 | A wise man has integrity, firmness of will, nobility, consistency, sobriety, patience [Cicero] |
| Full Idea: The wise man does nothing of which he can repent, nothing against his will, does everything nobly, consistently, soberly, rightly, not looking forward to anything as bound to come, is not astonished at any novel occurrence, abides by his own decisions. | |
| From: M. Tullius Cicero (Tusculan Disputations [c.44 BCE], V.xxviii) | |
| A reaction: Notice that the wise man never exhibits weakness of will (an Aristotelian virtue), and is consistent (as Kant proposed), and is patient (as the Stoics proposed). But Cicero doesn't think he should busy himself maximising happiness. |
| 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. |
| 23367 | Even pointing a finger should only be done for a reason [Epictetus] |
| Full Idea: Philosophy says it is not right even to stretch out a finger without some reason. | |
| From: Epictetus (fragments/reports [c.57], 15) | |
| A reaction: The key point here is that philosophy concerns action, an idea on which Epictetus is very keen. He rather despise theory. This idea perfectly sums up the concept of the wholly rational life (which no rational person would actually want to live!). |
| 5891 | Philosophy is the collection of rational arguments [Cicero] |
| Full Idea: Philosophy consists in the collection of rational arguments. [Philosophia ex rationum collatione constet] | |
| From: M. Tullius Cicero (Tusculan Disputations [c.44 BCE], IV.xxxviii.84) | |
| A reaction: A nice epigraph for this database. Philosophy is, I trust, a little more than that, because you don't just hide them away in a drawer. But if you arrange them nicely in a museum (a website, for example), not a lot more can be done. |
| 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. |
| 5879 | The soul is the heart, or blood in the heart, or part of the brain, of something living in heart or brain, or breath [Cicero] |
| Full Idea: Some think the soul is the heart; Empedocles holds that the soul is blood in the heart; others said one part of the brain claimed the primacy of soul; others say the heart or brain are habitations of the soul; while others identify soul and breath. | |
| From: M. Tullius Cicero (Tusculan Disputations [c.44 BCE], I.ix.17-19) | |
| A reaction: A nice survey of views. Note that many of them identify the psuché/anima with physical parts of the body; only the fourth option seems to be dualist. This is despite the contemptuous response to Democritus' atomist theory of soul. |
| 5884 | How can one mind perceive so many dissimilar sensations? [Cicero] |
| Full Idea: Why is it that, using the same mind, we have perception of things so utterly unlike as colour, taste, heat, smell and sound? | |
| From: M. Tullius Cicero (Tusculan Disputations [c.44 BCE], I.xx.47) | |
| A reaction: This leaves us with the 'binding problem', of how the dissimilar sensations are pulled together into one field of experience. It is a nice simple objection, though, to anyone who simplistically claims that the mind is self-evidently unified. |
| 5887 | The soul has a single nature, so it cannot be divided, and hence it cannot perish [Cicero] |
| Full Idea: In souls there is no mingling of ingredients, nothing of two-fold nature, so it is impossible for the soul to be divided; impossible, therefore, for it to perish either; for perishing is like the separation of parts which were maintained in union. | |
| From: M. Tullius Cicero (Tusculan Disputations [c.44 BCE], I.xxix.71) | |
| A reaction: Cicero knows he is pushing his luck in asserting that perishing is a sort of division. Why can't something be there one moment and gone the next? He appears to be in close agreement with Descartes about being a 'thinking thing'. |
| 5886 | Like the eye, the soul has no power to see itself, but sees other things [Cicero] |
| Full Idea: The soul has not the power of itself to see itself, but, like the eye, the soul, though it does not see itself, yet discerns other things. | |
| From: M. Tullius Cicero (Tusculan Disputations [c.44 BCE], I.xxvii) | |
| A reaction: The soul is a complex item which contributes many layers of interpretation to what it sees, so there is scope for parts of the soul seeing other parts. Somewhere in the middle Cicero seems to be right - there is an elusive something we can't get at. |
| 5885 | Souls contain no properties of elements, and elements contain no properties of souls [Cicero] |
| Full Idea: No beginnings of souls can be found on earth; there is no combination in souls that could be born from earth, nothing that partakes of moist or airy or fiery; for in those elements there is nothing to possess the power of memory, thought, or reflection. | |
| From: M. Tullius Cicero (Tusculan Disputations [c.44 BCE], I.xxvi.66) | |
| A reaction: Interesting, but I think magnetism is an instructive analogy, which has weird properties which we never perceive in elements (though it is there, buried deep - suggesting panpsychism). Cicero would be disconcerted to find that fire isn't an element. |
| 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. |
| 5890 | We should not share the distress of others, but simply try to relieve it [Cicero] |
| Full Idea: We ought not to share distresses ourselves for the sake of others, but we ought to relieve others of their distress if we can. | |
| From: M. Tullius Cicero (Tusculan Disputations [c.44 BCE], IV.xxvi.56) | |
| A reaction: This strikes me as a sensible and balanced attitude. Some people, particularly in a Christian culture, urge that feeling strong and painful compassion for others is an intrinsic good, but the commonsense view is that that just increases human suffering. |
| 5894 | All men except philosophers fear poverty [Cicero] |
| Full Idea: All men are afraid of poverty, but not a single philosopher is so. | |
| From: M. Tullius Cicero (Tusculan Disputations [c.44 BCE], V.xxxi.88) | |
| A reaction: Not a thought which is encountered very often in modern philosophy journals. If a person is to be 'philosophical' in the way they live, calm endurance of the vicissitudes and hardships of life has to be a key prerequisite. |
| 5895 | If one despises illiterate mechanics individually, they are not worth more collectively [Cicero] |
| Full Idea: Can anything be more foolish than to suppose that those, whom individually one despises as illiterate mechanics, are worth anything collectively? | |
| From: M. Tullius Cicero (Tusculan Disputations [c.44 BCE], V.xxxvi.104) | |
| A reaction: Aristotle disagrees (Idea 2823). In 1906 a huge number of people guessed the weight of a cow at a fair, and the average was within one pound of the truth. In our world the healthy workings of the group are warped by the mass media. |