18 ideas
| 14249 | Boolos reinterprets second-order logic as plural logic [Boolos, by Oliver/Smiley] |
| Full Idea: Boolos's conception of plural logic is as a reinterpretation of second-order logic. | |
| From: report of George Boolos (On Second-Order Logic [1975]) by Oliver,A/Smiley,T - What are Sets and What are they For? n5 | |
| A reaction: Oliver and Smiley don't accept this view, and champion plural reference differently (as, I think, some kind of metalinguistic device?). |
| 10830 | Second-order logic metatheory is set-theoretic, and second-order validity has set-theoretic problems [Boolos] |
| Full Idea: The metatheory of second-order logic is hopelessly set-theoretic, and the notion of second-order validity possesses many if not all of the epistemic debilities of the notion of set-theoretic truth. | |
| From: George Boolos (On Second-Order Logic [1975], p.45) | |
| A reaction: Epistemic problems arise when a logic is incomplete, because some of the so-called truths cannot be proved, and hence may be unreachable. This idea indicates Boolos's motivation for developing a theory of plural quantification. |
| 10829 | A sentence can't be a truth of logic if it asserts the existence of certain sets [Boolos] |
| Full Idea: One may be of the opinion that no sentence ought to be considered as a truth of logic if, no matter how it is interpreted, it asserts that there are sets of certain sorts. | |
| From: George Boolos (On Second-Order Logic [1975], p.44) | |
| A reaction: My intuition is that in no way should any proper logic assert the existence of anything at all. Presumably interpretations can assert the existence of numbers or sets, but we should be able to identify something which is 'pure' logic. Natural deduction? |
| 10832 | '∀x x=x' only means 'everything is identical to itself' if the range of 'everything' is fixed [Boolos] |
| Full Idea: One may say that '∀x x=x' means 'everything is identical to itself', but one must realise that one's answer has a determinate sense only if the reference (range) of 'everything' is fixed. | |
| From: George Boolos (On Second-Order Logic [1975], p.46) | |
| A reaction: This is the problem now discussed in the recent book 'Absolute Generality', of whether one can quantify without specifying a fixed or limited domain. |
| 10834 | Weak completeness: if it is valid, it is provable. Strong: it is provable from a set of sentences [Boolos] |
| Full Idea: A weak completeness theorem shows that a sentence is provable whenever it is valid; a strong theorem, that a sentence is provable from a set of sentences whenever it is a logical consequence of the set. | |
| From: George Boolos (On Second-Order Logic [1975], p.52) | |
| A reaction: So the weak version says |- φ → |= φ, and the strong versions says Γ |- φ → Γ |= φ. Presumably it is stronger if it can specify the source of the inference. |
| 13841 | Why should compactness be definitive of logic? [Boolos, by Hacking] |
| Full Idea: Boolos asks why on earth compactness, whatever its virtues, should be definitive of logic itself. | |
| From: report of George Boolos (On Second-Order Logic [1975]) by Ian Hacking - What is Logic? §13 |
| 10833 | Many concepts can only be expressed by second-order logic [Boolos] |
| Full Idea: The notions of infinity and countability can be characterized by second-order sentences, though not by first-order sentences (as compactness and Skolem-Löwenheim theorems show), .. as well as well-ordering, progression, ancestral and identity. | |
| From: George Boolos (On Second-Order Logic [1975], p.48) |
| 468 | Musical performance can reveal a range of virtues [Damon of Ath.] |
| Full Idea: In singing and playing the lyre, a boy will be likely to reveal not only courage and moderation, but also justice. | |
| From: Damon (fragments/reports [c.460 BCE], B4), quoted by (who?) - where? |
| 23529 | Conduct is not isolated from its effect on the moral code [Hart,HLA] |
| Full Idea: We must not view conduct in isolation from its effect on the moral code. | |
| From: H.L.A. Hart (Law,Liberty and Morality [1963], II 'Moderate') | |
| A reaction: The moral code may be excessively conservative, but there is no denying this point. Extreme individualistic libertarians must recognise that 'no man is an island'. |
| 23530 | The great danger of democracy is that the oppression of the minority becomes unobjectionable [Hart,HLA] |
| Full Idea: For Mill and De Tocqueville the greatest of the dangers was not that in fact the majority might use their power to oppress a minority, but that, with the spread of democratic ideas, it might come to be thought unobjectionable that they should do so. | |
| From: H.L.A. Hart (Law,Liberty and Morality [1963], III 'Populism') | |
| A reaction: This was vivid in the 2016 Brexit referendum, which was 52-48 in favour of leaving. There were lots voices saying 'you lost, get over it'. It should be a basic (if neglected) principle that the winners of elections now represent the whole population. |
| 23522 | In an organised society all actions have some effect on other people [Hart,HLA] |
| Full Idea: In an organised society it is impossible to identify classes of actions which harm no one, or no one but the individual who does them. | |
| From: H.L.A. Hart (Law,Liberty and Morality [1963], I 'Enforcement') | |
| A reaction: This is attributed to 'some critics' of Mill. I agree with this. The idea that actions performed behind close doors never come to influence social life is an illusion, held by people whose quest for freedom is selfish. |
| 23528 | The value of liberty allows freedom of action, even if that distresses other people [Hart,HLA] |
| Full Idea: Recognition of individual liberty as a value involves, as a minimum, acceptance of the principle that the individual may do what he wants, even if others are distressed when the learn what it is that he does. | |
| From: H.L.A. Hart (Law,Liberty and Morality [1963], II 'Private') | |
| A reaction: He notes that there could be other reasons to block the freedom, such as harm done. This idea seems to identify a key component of liberalism - that we must all tolerate actions which we dislike. |
| 23523 | The principle of legality requires crimes to be precisely defined in advance of any action [Hart,HLA] |
| Full Idea: The principle of legality requires criminal offences to be as precisely defined as possible, so that it can be known with reasonable certainty beforehand what acts are criminal and what are not. | |
| From: H.L.A. Hart (Law,Liberty and Morality [1963], I 'Conspiracy') | |
| A reaction: Hart is discussing a breach of this, where moral judgements are used to condemn something which was not obviously illegal. Families and schools don't have such precise rules, but it seems needed in a vast and pluralistic society. |
| 23524 | Some private moral issues are no concern of the law [Hart,HLA] |
| Full Idea: An official report [of 1957] on homosexuality declared that 'there must remain a realm of private morality and immorality which is, in brief and crude terms, not the law's business'. | |
| From: H.L.A. Hart (Law,Liberty and Morality [1963], I 'Conspiracy') | |
| A reaction: We might wonder whether these issues are actually moral, if the law is not interested in them. Are they just a matter of taste? The law doesn't enforce a preference for Mozart over Salieri. |
| 23521 | Do morals influence law? Is morality an aspect of law? Can law be morally criticised? [Hart,HLA] |
| Full Idea: Four questions: 1) Has the development of law been influenced by morals? 2) Must reference to morality enter into an adequate definition of law or legal system? 3) Is law open to moral criticism? 4) Does immorality justify legal punishment? | |
| From: H.L.A. Hart (Law,Liberty and Morality [1963], I 'Enforcement') | |
| A reaction: [compressed] Three nice questions, which are his agenda for the book. It is obvious that immoral laws can be created, and that laws can be criticised for being too concerned with morality, so there is no clear general answer to these dilemmas. |
| 23525 | Is the enforcement of morality morally justifiable? [Hart,HLA] |
| Full Idea: The question about morality and the law is also a question of morality - of whether the enforcement of morality is morally justified. | |
| From: H.L.A. Hart (Law,Liberty and Morality [1963], I 'Positive') | |
| A reaction: This is a very nice meta-moral question. What moral standards are used to justify the enforcement of moral standards? Presumably there should be no contradiction between the levels, to brutally enforce softness, or softly recommend brutality? |
| 23526 | Modern law still suppresses practices seen as immoral, and yet harmless [Hart,HLA] |
| Full Idea: English and American law still [in1963] contain rules which suppress practices condemned as immoral by positive morality though they involve nothing that would be ordinarily thought of as harm to other persons. | |
| From: H.L.A. Hart (Law,Liberty and Morality [1963], II 'Use') | |
| A reaction: He says most of the examples of this concern sexual practices. In the UK we have moved away from such laws, but many states of the USA still maintain them (or are reintroducing them, in 2023). |
| 23527 | Moral wickedness of an offence is always relevant to the degree of punishment [Hart,HLA] |
| Full Idea: Leslie Stephen argued that when the question is how severely an offender should be punished, an estimate of the degree of moral wickedness involved in the crime is always relevant. | |
| From: H.L.A. Hart (Law,Liberty and Morality [1963], II 'Moral') | |
| A reaction: [Stephen 'Liberty, Equality, Fraternity' 1873] The degree of responsibility (after excuses etc.) is obviously also highly relevant. If vicious murder is punished more harshly, that seems to be an assessment of the character of the murderer. |