29 ideas
| 7396 | Hobbes created English-language philosophy [Hobbes, by Tuck] |
| Full Idea: Hobbes created English-language philosophy. | |
| From: report of Thomas Hobbes (The Elements of Law [1640]) by Richard Tuck - Hobbes Pref | |
| A reaction: Tuck mentions Hooker as a predecessor in jurisprudence. Otherwise, an impressive label. |
| 10775 | The axiom of choice now seems acceptable and obvious (if it is meaningful) [Tharp] |
| Full Idea: The main objection to the axiom of choice was that it had to be given by some law or definition, but since sets are arbitrary this seems irrelevant. Formalists consider it meaningless, but set-theorists consider it as true, and practically obvious. | |
| From: Leslie H. Tharp (Which Logic is the Right Logic? [1975], §3) |
| 11211 | If a sound conclusion comes from two errors that cancel out, the path of the argument must matter [Rumfitt] |
| Full Idea: If a designated conclusion follows from the premisses, but the argument involves two howlers which cancel each other out, then the moral is that the path an argument takes from premisses to conclusion does matter to its logical evaluation. | |
| From: Ian Rumfitt ("Yes" and "No" [2000], II) | |
| A reaction: The drift of this is that our view of logic should be a little closer to the reasoning of ordinary language, and we should rely a little less on purely formal accounts. |
| 10766 | Logic is either for demonstration, or for characterizing structures [Tharp] |
| Full Idea: One can distinguish at least two quite different senses of logic: as an instrument of demonstration, and perhaps as an instrument for the characterization of structures. | |
| From: Leslie H. Tharp (Which Logic is the Right Logic? [1975], §2) | |
| A reaction: This is trying to capture the proof-theory and semantic aspects, but merely 'characterizing' something sounds like a rather feeble aspiration for the semantic side of things. Isn't it to do with truth, rather than just rule-following? |
| 10767 | Elementary logic is complete, but cannot capture mathematics [Tharp] |
| Full Idea: Elementary logic cannot characterize the usual mathematical structures, but seems to be distinguished by its completeness. | |
| From: Leslie H. Tharp (Which Logic is the Right Logic? [1975], §2) |
| 10769 | Second-order logic isn't provable, but will express set-theory and classic problems [Tharp] |
| Full Idea: The expressive power of second-order logic is too great to admit a proof procedure, but is adequate to express set-theoretical statements, and open questions such as the continuum hypothesis or the existence of big cardinals are easily stated. | |
| From: Leslie H. Tharp (Which Logic is the Right Logic? [1975], §2) |
| 11210 | Standardly 'and' and 'but' are held to have the same sense by having the same truth table [Rumfitt] |
| Full Idea: If 'and' and 'but' really are alike in sense, in what might that likeness consist? Some philosophers of classical logic will reply that they share a sense by virtue of sharing a truth table. | |
| From: Ian Rumfitt ("Yes" and "No" [2000]) | |
| A reaction: This is the standard view which Rumfitt sets out to challenge. |
| 11212 | The sense of a connective comes from primitively obvious rules of inference [Rumfitt] |
| Full Idea: A connective will possess the sense that it has by virtue of its competent users' finding certain rules of inference involving it to be primitively obvious. | |
| From: Ian Rumfitt ("Yes" and "No" [2000], III) | |
| A reaction: Rumfitt cites Peacocke as endorsing this view, which characterises the logical connectives by their rules of usage rather than by their pure semantic value. |
| 10762 | In sentential logic there is a simple proof that all truth functions can be reduced to 'not' and 'and' [Tharp] |
| Full Idea: In sentential logic there is a simple proof that all truth functions, of any number of arguments, are definable from (say) 'not' and 'and'. | |
| From: Leslie H. Tharp (Which Logic is the Right Logic? [1975], §0) | |
| A reaction: The point of 'say' is that it can be got down to two connectives, and these are just the usual preferred pair. |
| 10776 | The main quantifiers extend 'and' and 'or' to infinite domains [Tharp] |
| Full Idea: The symbols ∀ and ∃ may, to start with, be regarded as extrapolations of the truth functional connectives ∧ ('and') and ∨ ('or') to infinite domains. | |
| From: Leslie H. Tharp (Which Logic is the Right Logic? [1975], §5) |
| 10774 | There are at least five unorthodox quantifiers that could be used [Tharp] |
| Full Idea: One might add to one's logic an 'uncountable quantifier', or a 'Chang quantifier', or a 'two-argument quantifier', or 'Shelah's quantifier', or 'branching quantifiers'. | |
| From: Leslie H. Tharp (Which Logic is the Right Logic? [1975], §3) | |
| A reaction: [compressed - just listed for reference, if you collect quantifiers, like collecting butterflies] |
| 10777 | Skolem mistakenly inferred that Cantor's conceptions were illusory [Tharp] |
| Full Idea: Skolem deduced from the Löwenheim-Skolem theorem that 'the absolutist conceptions of Cantor's theory' are 'illusory'. I think it is clear that this conclusion would not follow even if elementary logic were in some sense the true logic, as Skolem assumed. | |
| From: Leslie H. Tharp (Which Logic is the Right Logic? [1975], §7) | |
| A reaction: [Tharp cites Skolem 1962 p.47] Kit Fine refers to accepters of this scepticism about the arithmetic of infinities as 'Skolemites'. |
| 10773 | The Löwenheim-Skolem property is a limitation (e.g. can't say there are uncountably many reals) [Tharp] |
| Full Idea: The Löwenheim-Skolem property seems to be undesirable, in that it states a limitation concerning the distinctions the logic is capable of making, such as saying there are uncountably many reals ('Skolem's Paradox'). | |
| From: Leslie H. Tharp (Which Logic is the Right Logic? [1975], §2) |
| 10765 | Soundness would seem to be an essential requirement of a proof procedure [Tharp] |
| Full Idea: Soundness would seem to be an essential requirement of a proof procedure, since there is little point in proving formulas which may turn out to be false under some interpretation. | |
| From: Leslie H. Tharp (Which Logic is the Right Logic? [1975], §2) |
| 10763 | Completeness and compactness together give axiomatizability [Tharp] |
| Full Idea: Putting completeness and compactness together, one has axiomatizability. | |
| From: Leslie H. Tharp (Which Logic is the Right Logic? [1975], §1) |
| 10770 | If completeness fails there is no algorithm to list the valid formulas [Tharp] |
| Full Idea: In general, if completeness fails there is no algorithm to list the valid formulas. | |
| From: Leslie H. Tharp (Which Logic is the Right Logic? [1975], §2) | |
| A reaction: I.e. the theory is not effectively enumerable. |
| 10771 | Compactness is important for major theories which have infinitely many axioms [Tharp] |
| Full Idea: It is strange that compactness is often ignored in discussions of philosophy of logic, since the most important theories have infinitely many axioms. | |
| From: Leslie H. Tharp (Which Logic is the Right Logic? [1975], §2) | |
| A reaction: An example of infinite axioms is the induction schema in first-order Peano Arithmetic. |
| 10772 | Compactness blocks infinite expansion, and admits non-standard models [Tharp] |
| Full Idea: The compactness condition seems to state some weakness of the logic (as if it were futile to add infinitely many hypotheses). To look at it another way, formalizations of (say) arithmetic will admit of non-standard models. | |
| From: Leslie H. Tharp (Which Logic is the Right Logic? [1975], §2) |
| 10764 | A complete logic has an effective enumeration of the valid formulas [Tharp] |
| Full Idea: A complete logic has an effective enumeration of the valid formulas. | |
| From: Leslie H. Tharp (Which Logic is the Right Logic? [1975], §2) |
| 10768 | Effective enumeration might be proved but not specified, so it won't guarantee knowledge [Tharp] |
| Full Idea: Despite completeness, the mere existence of an effective enumeration of the valid formulas will not, by itself, provide knowledge. For example, one might be able to prove that there is an effective enumeration, without being able to specify one. | |
| From: Leslie H. Tharp (Which Logic is the Right Logic? [1975], §2) | |
| A reaction: The point is that completeness is supposed to ensure knowledge (of what is valid but unprovable), and completeness entails effective enumerability, but more than the latter is needed to do the key job. |
| 16638 | The qualities of the world are mere appearances; reality is the motions which cause them [Hobbes] |
| Full Idea: Whatsoever accidents or qualities our senses make us think there be in the world, they are not there, but are seemings and apparitions only. The things that really are in the world without us are those motions by which these seemings are caused. | |
| From: Thomas Hobbes (The Elements of Law [1640], I.2.10), quoted by Robert Pasnau - Metaphysical Themes 1274-1671 10.2 | |
| A reaction: This seems to count as a sense-datum theory, rather than a representative theory of perception, since it makes no commitment to the qualities containing any accurate information at all. We just start from the qualities and try to work it out. |
| 16688 | Evidence is conception, which is imagination, which proceeds from the senses [Hobbes] |
| Full Idea: All evidence is conception, as it is said, and all conception is imagination and proceeds from sense. And spirits we suppose to be those substances which work not upon the sense, and therefore not conceptible. | |
| From: Thomas Hobbes (The Elements of Law [1640], I.11.5), quoted by Robert Pasnau - Metaphysical Themes 1274-1671 16.2 | |
| A reaction: This is exactly the same as Hume's claim that all ideas are the result of impressions, and is the very essence of empiricism. We see here that such an epistemology can have huge consequences. |
| 7405 | Experience can't prove universal truths [Hobbes] |
| Full Idea: Experience concludeth nothing universally. | |
| From: Thomas Hobbes (The Elements of Law [1640], I.4.10), quoted by Richard Tuck - Hobbes Ch.2 | |
| A reaction: Empiricists seem proud to claim this limitation on human understanding, where rationalists like Leibniz use it as an argument against empiricism. Kripke says (e.g. Idea 4966) they are both wrong! I sympathise with Kripke. |
| 11214 | We learn 'not' along with affirmation, by learning to either affirm or deny a sentence [Rumfitt] |
| Full Idea: The standard view is that affirming not-A is more complex than affirming the atomic sentence A itself, with the latter determining its sense. But we could learn 'not' directly, by learning at once how to either affirm A or reject A. | |
| From: Ian Rumfitt ("Yes" and "No" [2000], IV) | |
| A reaction: [compressed] This seems fairly anti-Fregean in spirit, because it looks at the psychology of how we learn 'not' as a way of clarifying what we mean by it, rather than just looking at its logical behaviour (and thus giving it a secondary role). |
| 7408 | It is an error that reason should control the passions, which give right guidance on their own [Hobbes, by Tuck] |
| Full Idea: Hobbes (and Descartes, and many contemporaries) argued that the traditional idea that reason should control the passions was an error, and that (properly understood) our emotions would guide us in the right direction. | |
| From: report of Thomas Hobbes (The Elements of Law [1640]) by Richard Tuck - Hobbes Ch.2 | |
| A reaction: I'm an intellectualist on this one. It strikes me as rather naïve and romantic to think that unthinking emotion could ever consistently approach what is right. A recipe for disaster. |
| 7407 | Good and evil are what please us; goodness and badness the powers causing them [Hobbes] |
| Full Idea: We call good and evil the things that please and displease us; and so we call goodness and badness, the qualities of powers whereby they do it. | |
| From: Thomas Hobbes (The Elements of Law [1640], I.7.3), quoted by Richard Tuck - Hobbes Ch.2 | |
| A reaction: It is pointed out by Tuck that this is just like his treatment of colour terms (values as secondary qualities). I would have thought it was obvious that I could say 'x pleases me, although I disapprove of it' (e.g. black humour). |
| 7410 | Self-preservation is basic, and people judge differently about that, implying ethical relativism [Hobbes, by Tuck] |
| Full Idea: If men are their own judges of what conduces to their preservation, ..all men make different decisions about what counts as a danger, so (for Hobbes) the grimmest version of ethical relativism seems to be the only possible ethical vision. | |
| From: report of Thomas Hobbes (The Elements of Law [1640]) by Richard Tuck - Hobbes Ch.2 | |
| A reaction: This might depend on self-preservation being the only fundamental value. But if self-preservation is not a pressing issue, presumably other values might come into play, some of them less concerned with the individual's own interests. |
| 7409 | Hobbes shifted from talk of 'the good' to talk of 'rights' [Hobbes, by Tuck] |
| Full Idea: Hobbes (like Grotius) shifted from talking about 'the good', which had been the traditional subject for both ancient and Renaissance moralists, to talking instead about 'rights'. | |
| From: report of Thomas Hobbes (The Elements of Law [1640]) by Richard Tuck - Hobbes Ch.2 | |
| A reaction: This is part of the crucial shift away from the Greek interest in excellence of character, towards the Enlightenment legalistic interest in right actions, as well as social rights. Bad move, well analysed by MacIntyre. |
| 7411 | The attributes of God just show our inability to conceive his nature [Hobbes] |
| Full Idea: All the attributes of God signify our inability and defect of power to conceive any thing concerning his nature. | |
| From: Thomas Hobbes (The Elements of Law [1640], I.10.2), quoted by Richard Tuck - Hobbes Ch.2 | |
| A reaction: Presumably he means that 'omnipotence' should just be translated as 'mind-boggling power'. St Anselm's concept of God (Idea 1405) is helpful here, placing it at the upper limit of what can actually be conceived. |