51 ideas
13520 | A 'tautology' must include connectives [Wolf,RS] |
Full Idea: 'For every number x, x = x' is not a tautology, because it includes no connectives. | |
From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 1.2) |
13524 | Deduction Theorem: T∪{P}|-Q, then T|-(P→Q), which justifies Conditional Proof [Wolf,RS] |
Full Idea: Deduction Theorem: If T ∪ {P} |- Q, then T |- (P → Q). This is the formal justification of the method of conditional proof (CPP). Its converse holds, and is essentially modus ponens. | |
From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 1.3) |
13522 | Universal Generalization: If we prove P(x) with no special assumptions, we can conclude ∀xP(x) [Wolf,RS] |
Full Idea: Universal Generalization: If we can prove P(x), only assuming what sort of object x is, we may conclude ∀xP(x) for the same x. | |
From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 1.3) | |
A reaction: This principle needs watching closely. If you pick one person in London, with no presuppositions, and it happens to be a woman, can you conclude that all the people in London are women? Fine in logic and mathematics, suspect in life. |
13521 | Universal Specification: ∀xP(x) implies P(t). True for all? Then true for an instance [Wolf,RS] |
Full Idea: Universal Specification: from ∀xP(x) we may conclude P(t), where t is an appropriate term. If something is true for all members of a domain, then it is true for some particular one that we specify. | |
From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 1.3) |
13523 | Existential Generalization (or 'proof by example'): if we can say P(t), then we can say something is P [Wolf,RS] |
Full Idea: Existential Generalization (or 'proof by example'): From P(t), where t is an appropriate term, we may conclude ∃xP(x). | |
From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 1.3) | |
A reaction: It is amazing how often this vacuous-sounding principles finds itself being employed in discussions of ontology, but I don't quite understand why. |
13529 | Empty Set: ∃x∀y ¬(y∈x). The unique empty set exists [Wolf,RS] |
Full Idea: Empty Set Axiom: ∃x ∀y ¬ (y ∈ x). There is a set x which has no members (no y's). The empty set exists. There is a set with no members, and by extensionality this set is unique. | |
From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 2.3) | |
A reaction: A bit bewildering for novices. It says there is a box with nothing in it, or a pair of curly brackets with nothing between them. It seems to be the key idea in set theory, because it asserts the idea of a set over and above any possible members. |
13526 | Comprehension Axiom: if a collection is clearly specified, it is a set [Wolf,RS] |
Full Idea: The comprehension axiom says that any collection of objects that can be clearly specified can be considered to be a set. | |
From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 2.2) | |
A reaction: This is virtually tautological, since I presume that 'clearly specified' means pinning down exact which items are the members, which is what a set is (by extensionality). The naïve version is, of course, not so hot. |
13534 | In first-order logic syntactic and semantic consequence (|- and |=) nicely coincide [Wolf,RS] |
Full Idea: One of the most appealing features of first-order logic is that the two 'turnstiles' (the syntactic single |-, and the semantic double |=), which are the two reasonable notions of logical consequence, actually coincide. | |
From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 5.3) | |
A reaction: In the excitement about the possibility of second-order logic, plural quantification etc., it seems easy to forget the virtues of the basic system that is the target of the rebellion. The issue is how much can be 'expressed' in first-order logic. |
13535 | First-order logic is weakly complete (valid sentences are provable); we can't prove every sentence or its negation [Wolf,RS] |
Full Idea: The 'completeness' of first order-logic does not mean that every sentence or its negation is provable in first-order logic. We have instead the weaker result that every valid sentence is provable. | |
From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 5.3) | |
A reaction: Peter Smith calls the stronger version 'negation completeness'. |
13519 | Model theory uses sets to show that mathematical deduction fits mathematical truth [Wolf,RS] |
Full Idea: Model theory uses set theory to show that the theorem-proving power of the usual methods of deduction in mathematics corresponds perfectly to what must be true in actual mathematical structures. | |
From: Robert S. Wolf (A Tour through Mathematical Logic [2005], Pref) | |
A reaction: That more or less says that model theory demonstrates the 'soundness' of mathematics (though normal arithmetic is famously not 'complete'). Of course, he says they 'correspond' to the truths, rather than entailing them. |
13531 | Model theory reveals the structures of mathematics [Wolf,RS] |
Full Idea: Model theory helps one to understand what it takes to specify a mathematical structure uniquely. | |
From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 5.1) | |
A reaction: Thus it is the development of model theory which has led to the 'structuralist' view of mathematics. |
13532 | Model theory 'structures' have a 'universe', some 'relations', some 'functions', and some 'constants' [Wolf,RS] |
Full Idea: A 'structure' in model theory has a non-empty set, the 'universe', as domain of variables, a subset for each 'relation', some 'functions', and 'constants'. | |
From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 5.2) |
13533 | First-order model theory rests on completeness, compactness, and the Löwenheim-Skolem-Tarski theorem [Wolf,RS] |
Full Idea: The three foundations of first-order model theory are the Completeness theorem, the Compactness theorem, and the Löwenheim-Skolem-Tarski theorem. | |
From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 5.3) | |
A reaction: On p.180 he notes that Compactness and LST make no mention of |- and are purely semantic, where Completeness shows the equivalence of |- and |=. All three fail for second-order logic (p.223). |
13537 | An 'isomorphism' is a bijection that preserves all structural components [Wolf,RS] |
Full Idea: An 'isomorphism' is a bijection between two sets that preserves all structural components. The interpretations of each constant symbol are mapped across, and functions map the relation and function symbols. | |
From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 5.4) |
13539 | The LST Theorem is a serious limitation of first-order logic [Wolf,RS] |
Full Idea: The Löwenheim-Skolem-Tarski theorem demonstrates a serious limitation of first-order logic, and is one of primary reasons for considering stronger logics. | |
From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 5.7) |
13538 | If a theory is complete, only a more powerful language can strengthen it [Wolf,RS] |
Full Idea: It is valuable to know that a theory is complete, because then we know it cannot be strengthened without passing to a more powerful language. | |
From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 5.5) |
13525 | Most deductive logic (unlike ordinary reasoning) is 'monotonic' - we don't retract after new givens [Wolf,RS] |
Full Idea: Deductive logic, including first-order logic and other types of logic used in mathematics, is 'monotonic'. This means that we never retract a theorem on the basis of new givens. If T|-φ and T⊆SW, then S|-φ. Ordinary reasoning is nonmonotonic. | |
From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 1.7) | |
A reaction: The classic example of nonmonotonic reasoning is the induction that 'all birds can fly', which is retracted when the bird turns out to be a penguin. He says nonmonotonic logic is a rich field in computer science. |
13530 | An ordinal is an equivalence class of well-orderings, or a transitive set whose members are transitive [Wolf,RS] |
Full Idea: Less theoretically, an ordinal is an equivalence class of well-orderings. Formally, we say a set is 'transitive' if every member of it is a subset of it, and an ordinal is a transitive set, all of whose members are transitive. | |
From: Robert S. Wolf (A Tour through Mathematical Logic [2005], 2.4) | |
A reaction: He glosses 'transitive' as 'every member of a member of it is a member of it'. So it's membership all the way down. This is the von Neumann rather than the Zermelo approach (which is based on singletons). |
13518 | Modern mathematics has unified all of its objects within set theory [Wolf,RS] |
Full Idea: One of the great achievements of modern mathematics has been the unification of its many types of objects. It began with showing geometric objects numerically or algebraically, and culminated with set theory representing all the normal objects. | |
From: Robert S. Wolf (A Tour through Mathematical Logic [2005], Pref) | |
A reaction: His use of the word 'object' begs all sorts of questions, if you are arriving from the street, where an object is something which can cause a bruise - but get used to it, because the word 'object' has been borrowed for new uses. |
4363 | The word 'person' is useless in ethics, because what counts as a good or bad self-conscious being? [Hursthouse] |
Full Idea: An excellent reason for keeping the word 'person' out of ethics is that it is usually so thinly defined that it cannot generate any sense of 'good person'. If a person is just a self-conscious being, what would count as a good or bad one? | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.9 n20) | |
A reaction: A nice point. Locke's concept of a person (rational self-conscious being) lacks depth and individuality, and Hitler fulfils the criteria as well as any saint. But if Hitler wasn't a 'bad person', what was he bad at being? |
4355 | There may be inverse akrasia, where the agent's action is better than their judgement recommends [Hursthouse] |
Full Idea: There seem to be cases of 'inverse akrasia', in which the course of action actually followed is superior to the course of action recommended by the agent's best judgement. | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.7) | |
A reaction: This must occur, as when an assassin lets his victim off, and then regrets the deed. It strengthens the case against Socrates, and in favour of their being two parts of the soul which compete to motivate our actions. |
4325 | Must all actions be caused in part by a desire, or can a belief on its own be sufficient? [Hursthouse] |
Full Idea: In contemporary philosophy of action, there is a fervid debate about whether any intentional action must be prompted in part by desire, or whether it is possible to be moved to action by a belief alone. | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Intro) | |
A reaction: I want a cool belief to be sufficient to produce an action, because it will permit at least a Kantian dimension to ethics, and make judgement central, and marginalise emotivism, which is the spawn of Satan. |
4351 | It is a fantasy that only through the study of philosophy can one become virtuous [Hursthouse] |
Full Idea: It is a fantasy that only through the study of philosophy can one become virtuous. | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.6) | |
A reaction: I personally believe that philosophy is the best route yet devised to the achievement of virtue, but it is clearly not essential. All the philosophers I meet are remarkably virtuous, but that may be a chicken/egg thing. |
4329 | After a moral dilemma is resolved there is still a 'remainder', requiring (say) regret [Hursthouse] |
Full Idea: When one moral requirement has overriden another in a dilemma, there is still a 'remainder', so that regret, or the recognition of some new requirement, are still appropriate. | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.2) | |
A reaction: This is a powerful point on behalf of virtue ethics. There is a correct way to feel about the application of rules and calculations. Judges sleep well at night, but virtuous people may not. |
4330 | Deontologists resolve moral dilemmas by saying the rule conflict is merely apparent [Hursthouse] |
Full Idea: With respect to resolvable dilemmas, the deontologist's strategy is to argue that the 'conflict' between the two rules which has generated the dilemma is merely apparent. | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.2) | |
A reaction: This assumes that the rules can't conflict (because they come for God, or pure reason), but we might say that there are correct rules which do conflict. Morality isn't physics, or tennis. |
4341 | Involuntary actions performed in tragic dilemmas are bad because they mar a good life [Hursthouse] |
Full Idea: The actions a virtuous agent is forced to in tragic dilemmas fail to be good actions because the doing of them, no matter how unwillingly or involuntarily, mars or ruins a good life. | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.3) | |
A reaction: Of course, only virtuous people have their lives ruined by such things. For the cold or the wicked it is just water off a duck's back. |
4340 | You are not a dishonest person if a tragic dilemma forces you to do something dishonest [Hursthouse] |
Full Idea: Doing what is, say, dishonest solely in the context of a tragic dilemma does not entail being dishonest, possessing that vice. | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.3 n8) | |
A reaction: This seems right, although it mustn't be thought that the dishonesty is thereby excused. Virtuous people find being dishonest very painful. |
4358 | Virtue may be neither sufficient nor necessary for eudaimonia [Hursthouse] |
Full Idea: Some critics say virtue is not necessary for eudaimonia (since the wicked sometimes flourish), and others say it is not sufficient (because virtuous behaviour sometimes ruins a life). | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.8) | |
A reaction: Both criticisms seem wrong (the wicked don't 'flourish', and complete virtue never ruins lives, except in tragic dilemmas). But it is hard to prove them wrong. |
4337 | Teenagers are often quite wise about ideals, but rather stupid about consequences [Hursthouse] |
Full Idea: Adolescents tend to be much more gormless about consequences than they are about ideals. | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.2 n12) | |
A reaction: Very accurate, I'm afraid. But this cuts both ways. They seem to need education not in virtue, but simply in consequences. |
4324 | Animals and plants can 'flourish', but only rational beings can have eudaimonia [Hursthouse] |
Full Idea: The trouble with 'flourishing' as a translation of 'eudaimonia' is that animals and even plants can flourish, but eudaimonia is possible only for rational beings. | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Intro) | |
A reaction: 'Flourishing' still seems better than 'happy', which is centrally used now to refer to a state of mind, not a situation. 'Well being' seems good, and plants are usually permitted that. |
4359 | When it comes to bringing up children, most of us think that the virtues are the best bet [Hursthouse] |
Full Idea: If you think about bringing up children to prepare them for life, rather than converting the wicked or convincing the moral sceptic, isn't virtue the most reliable bet? | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.8) | |
A reaction: A very convincing idea. They haven't the imagination to grasp consequences properly, or sufficient abstract thought to grasp principles, or the political cunning to negotiate contracts, but they can grasp ideals of what a good person is like. |
20195 | Eudaimonia first; virtue is a trait which promotes it; right acts are what virtues produce [Hursthouse, by Zagzebski] |
Full Idea: Hursthouse defines a virtue as a trait humans need to flourish or live well, ...so 'eudaimonia' is conceptually foundational, the concept of virtue is then derived, and the concept of a right act is derived from that. | |
From: report of Rosalind Hursthouse (Virtue Theory and Abortion [1992], p.226) by Linda Trinkaus Zagzebski - Virtues of the Mind II.1 | |
A reaction: Zagzebski is mapping different types of virtue theory. The purest theories say that virtue is intrinsically good. The others seem to be instrumental, in varying degrees. Zagzebski makes good motivations prior. |
4336 | Any strict ranking of virtues or rules gets abandoned when faced with particular cases [Hursthouse] |
Full Idea: Any codification ranking the virtues, like any codification ranking the rules, is bound to come up against cases where we will want to change the rankings. | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.2) | |
A reaction: This seems right, and yet it feels like a slippery slope. Am I supposed to be virtuous and wise, but have no principles? Infinite flexibility can lead straight to wickedness. Even the wise need something to hang on to. |
4334 | Virtue ethics is open to the objection that it fails to show priority among the virtues [Hursthouse] |
Full Idea: One criticism of virtue ethics is that it lamentably fails to come up with a priority ranking of the virtues. | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.2) | |
A reaction: However, one might refer to man's essential function, or characteristic function, and one might derive the virtues of a good citizen from the nature of a good society. |
4361 | Good animals can survive, breed, feel characteristic pleasure and pain, and contribute to the group [Hursthouse] |
Full Idea: A good social animal is well fitted for 1) individual survival, 2) continuance of its species, 3) characteristic freedom from pain and enjoyment, and 4) good characteristic functioning of its social group. | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.9) | |
A reaction: This feels right, but brings out the characteristic conservativism of virtue theory. A squirrel which can recite Shakespeare turns out to be immoral. |
4349 | Virtuous people may not be fully clear about their reasons for action [Hursthouse] |
Full Idea: Virtue must surely be compatible with a fair amount of inarticulacy about one's reasons for action. | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.6) | |
A reaction: Virtuous people may be unclear, but we are entitled to hope for clarification from moral philosophers. The least we can hope for is some distinction between virtue and vice. |
4352 | Performing an act simply because it is virtuous is sufficient to be 'morally motivated' or 'dutiful' [Hursthouse] |
Full Idea: Acting virtuously, in the way the virtuous agent acts, namely from virtue, is sufficient for being 'morally motivated' or acting 'from a sense of duty'. | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.7) | |
A reaction: Fine, but it invites the question of WHY virtue is motivating, just as one can ask this of maximum happiness, or duty, or even satisfaction of selfish desires. |
4353 | If moral motivation is an all-or-nothing sense of duty, how can children act morally? [Hursthouse] |
Full Idea: If you are inclined to think that 'moral motivation', acting because you think it is right, must be an all-or-nothing matter, its presence determined by the agent's mind at the moment of acting, do, please, remember children. | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.7) | |
A reaction: I agree about the vital importance of remembering children when discussing morality. However, Kantians might legitimately claim that when a child is simply trained to behave well, it has not yet reached the age of true morality. |
4346 | The emotions of sympathy, compassion and love are no guarantee of right action or acting well [Hursthouse] |
Full Idea: The emotions of sympathy, compassion and love are no guarantee of right action or acting well. | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.4) | |
A reaction: This is a critique of Hume, and of utlitarianism. It pushes us either to the concept of duty, or the concept of virtue (independent of right feeling). |
4339 | According to virtue ethics, two agents may respond differently, and yet both be right [Hursthouse] |
Full Idea: According to virtue ethics, in a given situation two different agents may do what is right, what gets a tick of approval, despite the fact that each fails to do what the other did. | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.3) | |
A reaction: You could certainly have great respect for two entirely different decisions about a medical dilemma, if they both showed integrity and good will, even if one had worse consequences than the other. |
4354 | Maybe in a deeply poisoned character none of their milder character traits could ever be a virtue [Hursthouse] |
Full Idea: I am prepare to stick my neck out and say that extreme Nazis or racists (say) have poisoned characters to such an extent that none of their character traits could ever count as a virtue. | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.7) | |
A reaction: Hard to justify, but it is hard to respect a mass murderer because they seem to love their dog or the beauty of music or flowers. They can't possibly appreciate the Platonic Form of love or beauty? |
4356 | We are puzzled by a person who can show an exceptional virtue and also behave very badly [Hursthouse] |
Full Idea: That we have some intuitive belief in the unity of the virtues is shown by our reaction to stories of a person who has shown an exceptional virtue, but also done something morally repellent. | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.7) | |
A reaction: A nice observation, but not enough to establish the unity of virtue. People tend to love all virtue, but it is not obviously impossible to love selected virtues and despise others (e.g. love courage, and despise charity). |
4364 | Being unusually virtuous in some areas may entail being less virtuous in others [Hursthouse] |
Full Idea: It may well be that being particularly well endowed with respect to some virtues inevitably involves being not very well endowed in others. | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.9) | |
A reaction: Maybe, but this sound a bit like an excuse. Newton wasn't very nice, but Einstein was. I can't believe in a finite reservoir of virtue. |
4327 | Deontologists do consider consequences, because they reveal when a rule might apply [Hursthouse] |
Full Idea: Though it is sometimes said that deontologists 'take no account of consequences', this is manifestly false, for many actions we deliberate about only fall under rules or principles when we bring in their predicted consequences. | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.1) | |
A reaction: An important defence of deontology, which otherwise is vulnerable to the 'well-meaning fool' problem. It is no good having a good will, but refusing to think about consequences. |
4335 | 'Codifiable' morality give rules for decisions which don't require wisdom [Hursthouse] |
Full Idea: If morality is strongly 'codifiable', it should consist of rules which provide a decision procedure, and it should be equally applicable by the virtuous and the non-virtuous, without recourse to wisdom. | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.2) | |
A reaction: A key idea. Religions want obedience, and Kant wants morality to be impersonal, and most people want morality which simple uneducated people can follow. And yet how can wisdom ever be irrelevant? |
4328 | Preference utilitarianism aims to be completely value-free, or empirical [Hursthouse] |
Full Idea: There are some forms of utilitarianism which aim to be entirely 'value-free' or empirical, such as those which define happiness in terms of the satisfaction of actual desires or preferences, regardless of their content. | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.1) | |
A reaction: This point makes it clear that preference utilitarianism is a doomed enterprise. For a start I can prefer not to be a utilitarian. You can only maximise something if you value if. Are preferences valuable? |
4338 | Deontologists usually accuse utilitarians of oversimplifying hard cases [Hursthouse] |
Full Idea: Deontologists characteristically maintain that utilitarians have made out a particular hard case to be too simple. | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.3) | |
A reaction: Utilitarianism certainly seems to ignore the anguish of hard dilemmas, but that is supposed to be its appeal. If you think for too long, every dilemma begins to seem hopeless. |
4343 | We are torn between utilitarian and deontological views of lying, depending on the examples [Hursthouse] |
Full Idea: Utilitarianism says there is nothing intrinsically wrong with lying, but examples of bare-faced lying to increase happiness drive us to deontology; but then examples where telling the truth has appalling consequences drive us back to utilitarianism again. | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.3) | |
A reaction: A nice illustration of why virtue theory suddenly seemed appealing. Deontology can cope, though, by seeing other duties when the consequences are dreadful. |
4365 | We are distinct from other animals in behaving rationally - pursuing something as good, for reasons [Hursthouse] |
Full Idea: Our characteristic way of going on, which distinguishes us from all the other species of animals, is a rational way, which is any way we can rightly see as good, as something we have reason to do. | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch10) | |
A reaction: Some people more than others, and none of us all the time. Romantics see rationality as a restraint on the authentic emotional and animal life. 'Be a good animal'. However, I agree. |
4350 | If people are virtuous in obedience to God, would they become wicked if they lost their faith? [Hursthouse] |
Full Idea: If people perform virtuous actions simply because they are commanded by God, would they cease to perform such actions if they lost their faith in God? | |
From: Rosalind Hursthouse (On Virtue Ethics [1999], Ch.6) | |
A reaction: To be consistent, the answer might be 'yes', but that invites the response that only intrinsically evil people need to be Christians. The rest of us can be good without it. |
9287 | Bruno said that ancient Egyptian magic was the true religion [Bruno, by Yates] |
Full Idea: Giordano Bruno maintained that the magical Egyptian religion of the world was not only the most ancient but also the only true religion, which both Judaism and Christianity had obscured and corrupted. | |
From: report of Giordano Bruno (works [1590]) by Frances A. Yates - Giordano Bruno and Hermetic Tradition Ch.1 | |
A reaction: His beliefs were based on the Hermetic writings. No wonder he was burned at the stake. Atheists now lay flowers at his memorial in Rome. The sixteenth century was when the hunt for alternatives to established religion began. |