21 ideas
| 13560 | A wise man is not subservient to anything [Seneca] |
| Full Idea: I do not call any man wise who is subservient to anything. | |
| From: Seneca the Younger (On the Happy Life [c.60], §11) | |
| A reaction: At the very least, a wise man should be subservient to a wiser man. |
| 7491 | The phases of human thought are theological, then metaphysical, then positivist [Comte, by Watson] |
| Full Idea: The first phase of humanity was theological, attributing phenomena to a deity, the second metaphysical stage attributed them to abstract forms, the third positive stage abandons ultimate causes and just searches for regularities. | |
| From: report of Auguste Comte (Course of Positive Philosophy [1846]) by Peter Watson - Ideas Ch.32 | |
| A reaction: This is obviously a highly empirical programme, which reasserts Hume's view of the laws of nature. Effectively, positivism just is the rejection of metaphysics. |
| 13838 | A decent modern definition should always imply a semantics [Hacking] |
| Full Idea: Today we expect that anything worth calling a definition should imply a semantics. | |
| From: Ian Hacking (What is Logic? [1979], §10) | |
| A reaction: He compares this with Gentzen 1935, who was attempting purely syntactic definitions of the logical connectives. |
| 13833 | 'Thinning' ('dilution') is the key difference between deduction (which allows it) and induction [Hacking] |
| Full Idea: 'Dilution' (or 'Thinning') provides an essential contrast between deductive and inductive reasoning; for the introduction of new premises may spoil an inductive inference. | |
| From: Ian Hacking (What is Logic? [1979], §06.2) | |
| A reaction: That is, inductive logic (if there is such a thing) is clearly non-monotonic, whereas classical inductive logic is monotonic. |
| 13834 | Gentzen's Cut Rule (or transitivity of deduction) is 'If A |- B and B |- C, then A |- C' [Hacking] |
| Full Idea: If A |- B and B |- C, then A |- C. This generalises to: If Γ|-A,Θ and Γ,A |- Θ, then Γ |- Θ. Gentzen called this 'cut'. It is the transitivity of a deduction. | |
| From: Ian Hacking (What is Logic? [1979], §06.3) | |
| A reaction: I read the generalisation as 'If A can be either a premise or a conclusion, you can bypass it'. The first version is just transitivity (which by-passes the middle step). |
| 13835 | Only Cut reduces complexity, so logic is constructive without it, and it can be dispensed with [Hacking] |
| Full Idea: Only the cut rule can have a conclusion that is less complex than its premises. Hence when cut is not used, a derivation is quite literally constructive, building up from components. Any theorem obtained by cut can be obtained without it. | |
| From: Ian Hacking (What is Logic? [1979], §08) |
| 13845 | The various logics are abstractions made from terms like 'if...then' in English [Hacking] |
| Full Idea: I don't believe English is by nature classical or intuitionistic etc. These are abstractions made by logicians. Logicians attend to numerous different objects that might be served by 'If...then', like material conditional, strict or relevant implication. | |
| From: Ian Hacking (What is Logic? [1979], §15) | |
| A reaction: The idea that they are 'abstractions' is close to my heart. Abstractions from what? Surely 'if...then' has a standard character when employed in normal conversation? |
| 13840 | First-order logic is the strongest complete compact theory with Löwenheim-Skolem [Hacking] |
| Full Idea: First-order logic is the strongest complete compact theory with a Löwenheim-Skolem theorem. | |
| From: Ian Hacking (What is Logic? [1979], §13) |
| 13844 | A limitation of first-order logic is that it cannot handle branching quantifiers [Hacking] |
| Full Idea: Henkin proved that there is no first-order treatment of branching quantifiers, which do not seem to involve any idea that is fundamentally different from ordinary quantification. | |
| From: Ian Hacking (What is Logic? [1979], §13) | |
| A reaction: See Hacking for an example of branching quantifiers. Hacking is impressed by this as a real limitation of the first-order logic which he generally favours. |
| 13842 | Second-order completeness seems to need intensional entities and possible worlds [Hacking] |
| Full Idea: Second-order logic has no chance of a completeness theorem unless one ventures into intensional entities and possible worlds. | |
| From: Ian Hacking (What is Logic? [1979], §13) |
| 13837 | With a pure notion of truth and consequence, the meanings of connectives are fixed syntactically [Hacking] |
| Full Idea: My doctrine is that the peculiarity of the logical constants resides precisely in that given a certain pure notion of truth and consequence, all the desirable semantic properties of the constants are determined by their syntactic properties. | |
| From: Ian Hacking (What is Logic? [1979], §09) | |
| A reaction: He opposes this to Peacocke 1976, who claims that the logical connectives are essentially semantic in character, concerned with the preservation of truth. |
| 13839 | Perhaps variables could be dispensed with, by arrows joining places in the scope of quantifiers [Hacking] |
| Full Idea: For some purposes the variables of first-order logic can be regarded as prepositions and place-holders that could in principle be dispensed with, say by a system of arrows indicating what places fall in the scope of which quantifier. | |
| From: Ian Hacking (What is Logic? [1979], §11) | |
| A reaction: I tend to think of variables as either pronouns, or as definite descriptions, or as temporary names, but not as prepositions. Must address this new idea... |
| 13843 | If it is a logic, the Löwenheim-Skolem theorem holds for it [Hacking] |
| Full Idea: A Löwenheim-Skolem theorem holds for anything which, on my delineation, is a logic. | |
| From: Ian Hacking (What is Logic? [1979], §13) | |
| A reaction: I take this to be an unusually conservative view. Shapiro is the chap who can give you an alternative view of these things, or Boolos. |
| 13558 | The supreme good is harmony of spirit [Seneca] |
| Full Idea: The highest good is harmony of spirit. | |
| From: Seneca the Younger (On the Happy Life [c.60], §08) | |
| A reaction: This idea is straight from Plato's Republic. |
| 13559 | I seek virtue, because it is its own reward [Seneca] |
| Full Idea: You ask what I seek from virtue? Virtue herself. For she has nothing better, she is herself her own reward. | |
| From: Seneca the Younger (On the Happy Life [c.60], §09) | |
| A reaction: Presumably this is the source of the popular saying that 'virtue is its own reward'. The trouble is that this doesn't seem a very persuasive thing to say to a sceptic who doubts whether being virtuous is worth the trouble. |
| 13561 | Virtue is always moderate, so excess need not be feared [Seneca] |
| Full Idea: In the case of virtue excess should not be feared, since in virtue resides moderation. | |
| From: Seneca the Younger (On the Happy Life [c.60], §13) | |
| A reaction: This seems to imply that all of the virtues are unified in the one achievement of the virtuous state. It leaves the notion of 'virtue' a bit thin in content, though. |
| 13562 | It is shameful to not even recognise your own slaves [Seneca] |
| Full Idea: Why, to your shame, are you so careless that you do not know your handful of slaves by sight? | |
| From: Seneca the Younger (On the Happy Life [c.60], §17) |
| 13564 | There is far more scope for virtue if you are wealthy; poverty only allows endurance [Seneca] |
| Full Idea: What doubt can there be that the wise man has greater scope for displaying his powers if he is rich than if he is poor, since in the case of poverty only one kind of virtue exists - refusal to be bowed down and crushed. | |
| From: Seneca the Younger (On the Happy Life [c.60], §22) | |
| A reaction: It is against this view that I see Jesus proposing poverty as central to virtue. But then he has the surprising view (to Seneca) that humility is a virtue. What Nietzsche calls the slaves' inversion of values. |
| 13563 | Why does your wife wear in her ears the income of a wealthy house? [Seneca] |
| Full Idea: Why does your wife wear in her ears the income of a wealthy house? | |
| From: Seneca the Younger (On the Happy Life [c.60], §17) |
| 13565 | If wealth was a good, it would make men good [Seneca] |
| Full Idea: Wealth is not a good; for it it was, it would make men good. | |
| From: Seneca the Younger (On the Happy Life [c.60], §24) | |
| A reaction: An immediately attractive argument, but should we assume that anything which is good will enhance our personal goodness? If goodness is a habit, then continual pursuit of wealth is the test case to examine. Seneca is right! |
| 13557 | Unfortunately the majority do not tend to favour what is best [Seneca] |
| Full Idea: Human concerns are not so happily arranged that the majority favours the better things. | |
| From: Seneca the Younger (On the Happy Life [c.60], §02) | |
| A reaction: On the whole Seneca is unimpressed by democracy, as people are rushed into decisions by the crowd, and live to regret them. |