32 ideas
| 7823 | Lucretius was rediscovered in 1417 [Grayling] |
| Full Idea: Lucretius's 'De Rerum Natura' was rediscovered in 1417, after languishing forgotten for six centuries. | |
| From: A.C. Grayling (What is Good? [2003], Ch.5) | |
| A reaction: A wonder. Is it the greatest book of the ancient world - because it partially preserves the lost philosophy of great Democritus? |
| 10751 | Second-order logic needs the sets, and its consequence has epistemological problems [Rossberg] |
| Full Idea: Second-order logic raises doubts because of its ontological commitment to the set-theoretic hierarchy, and the allegedly problematic epistemic status of the second-order consequence relation. | |
| From: Marcus Rossberg (First-order Logic, 2nd-order, Completeness [2004], §1) | |
| A reaction: The 'epistemic' problem is whether you can know the truths, given that the logic is incomplete, and so they cannot all be proved. Rossberg defends second-order logic against the second problem. A third problem is that it may be mathematics. |
| 10757 | Henkin semantics has a second domain of predicates and relations (in upper case) [Rossberg] |
| Full Idea: Henkin semantics (for second-order logic) specifies a second domain of predicates and relations for the upper case constants and variables. | |
| From: Marcus Rossberg (First-order Logic, 2nd-order, Completeness [2004], §3) | |
| A reaction: This second domain is restricted to predicates and relations which are actually instantiated in the model. Second-order logic is complete with this semantics. Cf. Idea 10756. |
| 10759 | There are at least seven possible systems of semantics for second-order logic [Rossberg] |
| Full Idea: In addition to standard and Henkin semantics for second-order logic, one might also employ substitutional or game-theoretical or topological semantics, or Boolos's plural interpretation, or even a semantics inspired by Lesniewski. | |
| From: Marcus Rossberg (First-order Logic, 2nd-order, Completeness [2004], §3) | |
| A reaction: This is helpful in seeing the full picture of what is going on in these logical systems. |
| 10753 | Logical consequence is intuitively semantic, and captured by model theory [Rossberg] |
| Full Idea: Logical consequence is intuitively taken to be a semantic notion, ...and it is therefore the formal semantics, i.e. the model theory, that captures logical consequence. | |
| From: Marcus Rossberg (First-order Logic, 2nd-order, Completeness [2004], §2) | |
| A reaction: If you come at the issue from normal speech, this seems right, but if you start thinking about the necessity of logical consequence, that formal rules and proof-theory seem to be the foundation. |
| 10752 | Γ |- S says S can be deduced from Γ; Γ |= S says a good model for Γ makes S true [Rossberg] |
| Full Idea: Deductive consequence, written Γ|-S, is loosely read as 'the sentence S can be deduced from the sentences Γ', and semantic consequence Γ|=S says 'all models that make Γ true make S true as well'. | |
| From: Marcus Rossberg (First-order Logic, 2nd-order, Completeness [2004], §2) | |
| A reaction: We might read |= as 'true in the same model as'. What is the relation, though, between the LHS and the RHS? They seem to be mutually related to some model, but not directly to one another. |
| 10754 | In proof-theory, logical form is shown by the logical constants [Rossberg] |
| Full Idea: A proof-theorist could insist that the logical form of a sentence is exhibited by the logical constants that it contains. | |
| From: Marcus Rossberg (First-order Logic, 2nd-order, Completeness [2004], §2) | |
| A reaction: You have to first get to the formal logical constants, rather than the natural language ones. E.g. what is the truth table for 'but'? There is also the matter of the quantifiers and the domain, and distinguishing real objects and predicates from bogus. |
| 10756 | A model is a domain, and an interpretation assigning objects, predicates, relations etc. [Rossberg] |
| Full Idea: A standard model is a set of objects called the 'domain', and an interpretation function, assigning objects in the domain to names, subsets to predicate letters, subsets of the Cartesian product of the domain with itself to binary relation symbols etc. | |
| From: Marcus Rossberg (First-order Logic, 2nd-order, Completeness [2004], §3) | |
| A reaction: The model actually specifies which objects have which predicates, and which objects are in which relations. Tarski's account of truth in terms of 'satisfaction' seems to be just a description of those pre-decided facts. |
| 10758 | If models of a mathematical theory are all isomorphic, it is 'categorical', with essentially one model [Rossberg] |
| Full Idea: A mathematical theory is 'categorical' if, and only if, all of its models are isomorphic. Such a theory then essentially has just one model, the standard one. | |
| From: Marcus Rossberg (First-order Logic, 2nd-order, Completeness [2004], §3) | |
| A reaction: So the term 'categorical' is gradually replacing the much-used phrase 'up to isomorphism'. |
| 10761 | Completeness can always be achieved by cunning model-design [Rossberg] |
| Full Idea: All that should be required to get a semantics relative to which a given deductive system is complete is a sufficiently cunning model-theorist. | |
| From: Marcus Rossberg (First-order Logic, 2nd-order, Completeness [2004], §5) |
| 10755 | A deductive system is only incomplete with respect to a formal semantics [Rossberg] |
| Full Idea: No deductive system is semantically incomplete in and of itself; rather a deductive system is incomplete with respect to a specified formal semantics. | |
| From: Marcus Rossberg (First-order Logic, 2nd-order, Completeness [2004], §3) | |
| A reaction: This important point indicates that a system might be complete with one semantics and incomplete with another. E.g. second-order logic can be made complete by employing a 'Henkin semantics'. |
| 6408 | Russell needed three extra axioms to reduce maths to logic: infinity, choice and reducibility [Grayling] |
| Full Idea: In order to deduce the theorems of mathematics from purely logical axioms, Russell had to add three new axioms to those of standards logic, which were: the axiom of infinity, the axiom of choice, and the axiom of reducibility. | |
| From: A.C. Grayling (Russell [1996], Ch.2) | |
| A reaction: The third one was adopted to avoid his 'barber' paradox, but many thinkers do not accept it. The interesting question is why anyone would 'accept' or 'reject' an axiom. |
| 6414 | Two propositions might seem self-evident, but contradict one another [Grayling] |
| Full Idea: Two propositions might contradict each other despite appearing self-evident when considered separately. | |
| From: A.C. Grayling (Russell [1996], Ch.2) | |
| A reaction: Russell's proposal (Idea 5416) is important here, that self-evidence comes in degrees. If self-evidence was all-or-nothing, Grayling's point would be a major problem, but it isn't. Bonjour explores the idea more fully (e.g. Idea 3704) |
| 7091 | The argument from analogy is not a strong inference, since the other being might be an actor or a robot [Grayling] |
| Full Idea: The argument from analogy is a weak one, because it does not logically guarantee the inference I draw to the other's inner states, for he might be dissimulating or acting, or may even be a cleverly contrived robot which feels nothing. | |
| From: A.C. Grayling (Wittgenstein [1988], Ch.3) | |
| A reaction: This gives the impression that for an argument to be strong it must logically guarantee its inference. It strikes me that analogy is a good reason for believing in other minds, but that is because I am looking for the best explanation, not logical proof. |
| 7293 | It is legitimate to do harm if it is the unintended side-effect of an effort to achieve a good [Grayling] |
| Full Idea: The doctrine of double effect says that it is legitimate to do harm if the harm is the unintended side-effect of an effort to achieve a legitimate goal. | |
| From: A.C. Grayling (Among the Dead Cities [2006], Ch.6) | |
| A reaction: I think a key principle of morality is our duty to think about possible unnoticed consequences of our actions. To neglect concern for side-effects is wicked. Beyond that, the issue must concern the particulars of the situation. |
| 7809 | In an honour code shame is the supreme punishment, and revenge is a duty [Grayling] |
| Full Idea: An honour code is one in which the greatest punishment is shame, and in which revenge is a duty. | |
| From: A.C. Grayling (What is Good? [2003], Ch.2) | |
| A reaction: Is this really what Nietzsche wanted to revive? Shame isn't a private matter - it needs solidarity of values in the community, and contempt for dishonour, so that it becomes everyone's worst fear. |
| 23262 | Experience, sympathy and history are sensible grounds for laying claim to rights [Grayling] |
| Full Idea: Personal experience, social sympathies, and history together licence laying claim to rights …which we see to make good mutual as well as individual sense. | |
| From: A.C. Grayling (The Good State [2020], 6) | |
| A reaction: There are no such thing as natural rights, but there are clearly natural grounds on which it is very reasonable to base a claim for legal rights. If positive rights are just arbitrary, or expressions of power struggles, that is crazy. |
| 23263 | Politics is driven by power cliques [Grayling] |
| Full Idea: What drives political history is power cliques. | |
| From: A.C. Grayling (The Good State [2020], Conc) | |
| A reaction: A simple ideas which strikes me as accurate. Alternative views are that power is universally distributed (Foucault), or that power resides in a social class (Marx). Grayling's idea strikes me as more accurate. Each class has its cliques. |
| 23255 | It is essential for democracy that voting is free and well informed [Grayling] |
| Full Idea: A necessary condition for democracy to be realised is that the act of voting should be free and informed. | |
| From: A.C. Grayling (The Good State [2020], p.25) | |
| A reaction: The requirement that voters should be well informed has become an increasing modern problem, because the media are owned by the wealthy, and false rumours can spread at lightning speed. |
| 23254 | Democracies should require a supermajority for major questions [Grayling] |
| Full Idea: A threshhold or supermajority bar (such as 60%) is the appropriate way to deal with highly consequential questions. | |
| From: A.C. Grayling (The Good State [2020], p.23) | |
| A reaction: This seems to be a very conservative view, because rejection of a major change is a decision in favour of the status quo. Would this rule apply equally to abolishing capital punishment and to reintroducing it? |
| 23260 | A cap on time of service would restrict party control and career ambitions [Grayling] |
| Full Idea: A method by which legislators can be rendered independent of both party control and career ambitions is a cap on the amount of time they can serve as legislators. | |
| From: A.C. Grayling (The Good State [2020], 4) | |
| A reaction: The time of service must allow for learning the job, and then using the wisdom of experience. Presumably some career ambitions are needed if we are to have leaders. Not all party discipline is bad; great achievements are hard without it. |
| 23253 | Majority decisions are only acceptable if the minority interests are not vital [Grayling] |
| Full Idea: A majority being in favour of some course of action is the acceptable means of reaching decisions when no vital interest of a minority is endangered. | |
| From: A.C. Grayling (The Good State [2020], 1) | |
| A reaction: This is generally accepted in extreme cases, such as the majority voting to exterminate the minority. The difficulty is to decide what is a 'vital' interest, and to get the majority to care about it. |
| 22595 | Liberty is the triumph of the individual, over both despotic government and enslaving majorities [Constant] |
| Full Idea: Lliberty is the triumph of the individual, as much over a government which seeks to rule by despotic methods, as over the masses who seek to render the minority the slave of the majority. | |
| From: Benjamin Constant (Principles of Politics [1806]), quoted by Ian Dunt - How to be a Liberal 4 | |
| A reaction: [No page given] Dunt describes Constant's book as the first really systematic account of liberalism. Very important to have rights against the majority, as well as against government. |
| 22597 | Minority rights are everyone's rights, because we all have turns in the minority [Constant] |
| Full Idea: To defend the rights of minorities is to defend the rights of all. Everyone in turn finds himself in the minority. | |
| From: Benjamin Constant (Principles of Politics [1806]), quoted by Ian Dunt - How to be a Liberal 4 | |
| A reaction: Very conformist people, who are often the most oppressive, are rarely in the minority, and are unlikely to be impressed by this idea. |
| 23256 | Liberty and equality cannot be reconciled [Grayling] |
| Full Idea: Liberty and equality appear to be irresolvable contradictions. | |
| From: A.C. Grayling (The Good State [2020], 2) | |
| A reaction: [He particularly cites Isaiah Berlin for this view] Hm. The liberty of one is the liberty of all. I don't think I would feel that my liberty was unreasonably infringed if I lived in a society of imposed equality. The greedy hate equality the most. |
| 23258 | The very concept of democracy entails a need for justice [Grayling] |
| Full Idea: The concept of democracy - embodying the principles of participation and equal concern - entails that social justice is a mandatory aim. | |
| From: A.C. Grayling (The Good State [2020], 2) | |
| A reaction: The idea that democracy entails participation in any direct way is what the right wing reject. Sustained participation would presumably entail various sorts of justice. |
| 23259 | There should be separate legislative, executive and judicial institutions [Grayling] |
| Full Idea: The obvious solution is where the legislative, executive and judicial powers are exercised by different institutions, distinguished by function. The executive is answerable to the legislative, and the judicial is controlled by neither. | |
| From: A.C. Grayling (The Good State [2020], 3) | |
| A reaction: Separation by institution, rather than merely by separate individuals exercising the powers. I agree (with Popper etc) that institutions are the way to secure long-term success and justice. Grayling says the judiciary must not paralyse government. |
| 7292 | War must also have a good chance of success, and be waged with moderation [Grayling] |
| Full Idea: To Aquinas's three conditions for war (Idea 7291) modern theorists have added two others: that to be just a war must have a reasonable chance of success, and that the means used to conduct it must be proportional to the ends sought. | |
| From: A.C. Grayling (Among the Dead Cities [2006], Ch.6) | |
| A reaction: These two principles strike me as being much more civilized and humane than Aquinas's original contribution, suggesting that in our theoretical thinking we might be making some progress. |
| 7824 | If suicide is lawful, but assisting suicide is unlawful, powerless people are denied their rights [Grayling] |
| Full Idea: An anomaly created by England's 1961 Suicide Act is that it is lawful to take one's own life, but unlawful to help anyone else to do it. This means anyone unable to commit suicide without help is denied one of their fundamental rights. | |
| From: A.C. Grayling (What is Good? [2003], Ch.8) | |
| A reaction: There is a difference, not really captured either by law or by reason, between tolerating an activity, and encouraging and helping it. I think the test question is "this activity is legal, but would you want your child to do it?" |
| 7819 | Religion gives answers, comforts, creates social order, and panders to superstition [Grayling] |
| Full Idea: The four standard explanations given for religion are that it provides answer, that it gives comfort, that it makes for social order, and that it rests on mere superstition. | |
| From: A.C. Grayling (What is Good? [2003], Ch.4) | |
| A reaction: All four of these could be correct, though the first and fourth would be incompatible if religion gives correct answers. Why religion begins might be not the same as the reason why it continues. |
| 7817 | To make an afterlife appealing, this life has to be denigrated [Grayling] |
| Full Idea: It is remarkable how much the life of this world has to be denigrated to make the promise of happiness after death appealing. | |
| From: A.C. Grayling (What is Good? [2003], Ch.4) | |
| A reaction: This seems to be true of most religions, but it could be otherwise. Surely you want such a wonderful life to continue after death? But then you would not be obliged to do anything difficult to achieve immortality. Power comes into it... |
| 7818 | In Greek mythology only heroes can go to heaven [Grayling] |
| Full Idea: In Greek mythology only a hero like Hercules could hope to go to heaven (by becoming a god himself). | |
| From: A.C. Grayling (What is Good? [2003], Ch.4) | |
| A reaction: This illustrates Nietsche's 'inversion of morality' most clearly, because Christianity says that the person most likely to go to heaven is the humblest person. |