61 ideas
| 125 | Is a gifted philosopher unmanly if he avoids the strife of the communal world? [Plato] |
| Full Idea: Callicles: Even a naturally gifted philosopher isn't going to develop into a real man, because he's avoiding the heart of his community and the thick of the agora. | |
| From: Plato (Gorgias [c.387 BCE], 485d) | |
| A reaction: A serious charge against philosophy. An attraction of the subject is its purity, its necessity, its timelessness, and in some ways these are just nicer and easier and more understandable than the hard mess of real life. But understanding has to be good. |
| 6806 | Do not multiply entities beyond necessity [William of Ockham] |
| Full Idea: Do not multiply entities beyond necessity. | |
| From: William of Ockham (works [1335]) | |
| A reaction: This is the classic statement of Ockham's Razor, though it is not found in his printed works. It appears to be mainly aimed at Plato's Theory of Forms. It is taken to refer to types of entities, not numbers. One seraph is as bad as a hundred. |
| 1654 | In "Gorgias" Socrates is confident that his 'elenchus' will decide moral truth [Vlastos on Plato] |
| Full Idea: In the 'Gorgias' Socrates is still supremely confident that the elenchus is the final arbiter of moral truth. | |
| From: comment on Plato (Gorgias [c.387 BCE]) by Gregory Vlastos - Socrates: Ironist and Moral Philosopher p.117 |
| 4321 | We should test one another, by asking and answering questions [Plato] |
| Full Idea: Test me, and let yourself be tested as well, by asking and answering questions. | |
| From: Plato (Gorgias [c.387 BCE], 462a) | |
| A reaction: The idea must be to avoid wild speculation, by continually filtering ideas through rival critical intelligences. The best philosophical method ever devised. |
| 9724 | Until the 1960s the only semantics was truth-tables [Enderton] |
| Full Idea: Until the 1960s standard truth-table semantics were the only ones that there were. | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], 1.10.1) | |
| A reaction: The 1960s presumably marked the advent of possible worlds. |
| 9703 | 'dom R' indicates the 'domain' of objects having a relation [Enderton] |
| Full Idea: 'dom R' indicates the 'domain' of a relation, that is, the set of all objects that are members of ordered pairs and that have that relation. | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
| 9705 | 'fld R' indicates the 'field' of all objects in the relation [Enderton] |
| Full Idea: 'fld R' indicates the 'field' of a relation, that is, the set of all objects that are members of ordered pairs on either side of the relation. | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
| 9704 | 'ran R' indicates the 'range' of objects being related to [Enderton] |
| Full Idea: 'ran R' indicates the 'range' of a relation, that is, the set of all objects that are members of ordered pairs and that are related to by the first objects. | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
| 9710 | We write F:A→B to indicate that A maps into B (the output of F on A is in B) [Enderton] |
| Full Idea: We write F : A → B to indicate that A maps into B, that is, the domain of relating things is set A, and the things related to are all in B. If we add that F = B, then A maps 'onto' B. | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
| 9707 | 'F(x)' is the unique value which F assumes for a value of x [Enderton] |
|
Full Idea:
F(x) is a 'function', which indicates the unique value which y takes in |
|
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
| 9712 | A relation is 'symmetric' on a set if every ordered pair has the relation in both directions [Enderton] |
| Full Idea: A relation is 'symmetric' on a set if every ordered pair in the set has the relation in both directions. | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
| 9713 | A relation is 'transitive' if it can be carried over from two ordered pairs to a third [Enderton] |
| Full Idea: A relation is 'transitive' on a set if the relation can be carried over from two ordered pairs to a third. | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
| 9699 | The 'powerset' of a set is all the subsets of a given set [Enderton] |
| Full Idea: The 'powerset' of a set is all the subsets of a given set. Thus: PA = {x : x ⊆ A}. | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
| 9700 | Two sets are 'disjoint' iff their intersection is empty [Enderton] |
| Full Idea: Two sets are 'disjoint' iff their intersection is empty (i.e. they have no members in common). | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
| 9702 | A 'domain' of a relation is the set of members of ordered pairs in the relation [Enderton] |
| Full Idea: The 'domain' of a relation is the set of all objects that are members of ordered pairs that are members of the relation. | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
| 9701 | A 'relation' is a set of ordered pairs [Enderton] |
| Full Idea: A 'relation' is a set of ordered pairs. The ordering relation on the numbers 0-3 is captured by - in fact it is - the set of ordered pairs {<0,1>,<0,2>,<0,3>,<1,2>,<1,3>,<2,3>}. | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) | |
| A reaction: This can't quite be a definition of order among numbers, since it relies on the notion of a 'ordered' pair. |
| 9706 | A 'function' is a relation in which each object is related to just one other object [Enderton] |
| Full Idea: A 'function' is a relation which is single-valued. That is, for each object, there is only one object in the function set to which that object is related. | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
| 9708 | A function 'maps A into B' if the relating things are set A, and the things related to are all in B [Enderton] |
| Full Idea: A function 'maps A into B' if the domain of relating things is set A, and the things related to are all in B. | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
| 9709 | A function 'maps A onto B' if the relating things are set A, and the things related to are set B [Enderton] |
| Full Idea: A function 'maps A onto B' if the domain of relating things is set A, and the things related to are set B. | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
| 9711 | A relation is 'reflexive' on a set if every member bears the relation to itself [Enderton] |
| Full Idea: A relation is 'reflexive' on a set if every member of the set bears the relation to itself. | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
| 9714 | A relation satisfies 'trichotomy' if all pairs are either relations, or contain identical objects [Enderton] |
| Full Idea: A relation satisfies 'trichotomy' on a set if every ordered pair is related (in either direction), or the objects are identical. | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
| 9717 | A set is 'dominated' by another if a one-to-one function maps the first set into a subset of the second [Enderton] |
| Full Idea: A set is 'dominated' by another if a one-to-one function maps the first set into a subset of the second. | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
| 9715 | An 'equivalence relation' is a reflexive, symmetric and transitive binary relation [Enderton] |
| Full Idea: An 'equivalence relation' is a binary relation which is reflexive, and symmetric, and transitive. | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
| 9716 | We 'partition' a set into distinct subsets, according to each relation on its objects [Enderton] |
| Full Idea: Equivalence classes will 'partition' a set. That is, it will divide it into distinct subsets, according to each relation on the set. | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
| 9722 | Inference not from content, but from the fact that it was said, is 'conversational implicature' [Enderton] |
| Full Idea: The process is dubbed 'conversational implicature' when the inference is not from the content of what has been said, but from the fact that it has been said. | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], 1.7.3) |
| 9718 | Validity is either semantic (what preserves truth), or proof-theoretic (following procedures) [Enderton] |
| Full Idea: The point of logic is to give an account of the notion of validity,..in two standard ways: the semantic way says that a valid inference preserves truth (symbol |=), and the proof-theoretic way is defined in terms of purely formal procedures (symbol |-). | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], 1.1.3..) | |
| A reaction: This division can be mirrored in mathematics, where it is either to do with counting or theorising about things in the physical world, or following sets of rules from axioms. Language can discuss reality, or play word-games. |
| 9721 | A logical truth or tautology is a logical consequence of the empty set [Enderton] |
| Full Idea: A is a logical truth (tautology) (|= A) iff it is a semantic consequence of the empty set of premises (φ |= A), that is, every interpretation makes A true. | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], 1.3.4) | |
| A reaction: So the final column of every line of the truth table will be T. |
| 9994 | A truth assignment to the components of a wff 'satisfy' it if the wff is then True [Enderton] |
| Full Idea: A truth assignment 'satisfies' a formula, or set of formulae, if it evaluates as True when all of its components have been assigned truth values. | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], 1.2) | |
| A reaction: [very roughly what Enderton says!] The concept becomes most significant when a large set of wff's is pronounced 'satisfied' after a truth assignment leads to them all being true. |
| 9719 | A proof theory is 'sound' if its valid inferences entail semantic validity [Enderton] |
| Full Idea: If every proof-theoretically valid inference is semantically valid (so that |- entails |=), the proof theory is said to be 'sound'. | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], 1.1.7) |
| 9720 | A proof theory is 'complete' if semantically valid inferences entail proof-theoretic validity [Enderton] |
| Full Idea: If every semantically valid inference is proof-theoretically valid (so that |= entails |-), the proof-theory is said to be 'complete'. | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], 1.1.7) |
| 9995 | Proof in finite subsets is sufficient for proof in an infinite set [Enderton] |
| Full Idea: If a wff is tautologically implied by a set of wff's, it is implied by a finite subset of them; and if every finite subset is satisfiable, then so is the whole set of wff's. | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], 2.5) | |
| A reaction: [Enderton's account is more symbolic] He adds that this also applies to models. It is a 'theorem' because it can be proved. It is a major theorem in logic, because it brings the infinite under control, and who doesn't want that? |
| 9996 | Expressions are 'decidable' if inclusion in them (or not) can be proved [Enderton] |
| Full Idea: A set of expressions is 'decidable' iff there exists an effective procedure (qv) that, given some expression, will decide whether or not the expression is included in the set (i.e. doesn't contradict it). | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], 1.7) | |
| A reaction: This is obviously a highly desirable feature for a really reliable system of expressions to possess. All finite sets are decidable, but some infinite sets are not. |
| 9997 | For a reasonable language, the set of valid wff's can always be enumerated [Enderton] |
| Full Idea: The Enumerability Theorem says that for a reasonable language, the set of valid wff's can be effectively enumerated. | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], 2.5) | |
| A reaction: There are criteria for what makes a 'reasonable' language (probably specified to ensure enumerability!). Predicates and functions must be decidable, and the language must be finite. |
| 22132 | Species and genera are individual concepts which naturally signify many individuals [William of Ockham] |
| Full Idea: In his mature nominalism, species and genera are identified with certain mental qualities called concepts or intentions of the mind. Ontologically they are individuals too, like everthing else, ...but they naturally signify many different individuals. | |
| From: William of Ockham (works [1335]), quoted by Claude Panaccio - William of Ockham p.1056 | |
| A reaction: 'Naturally' is the key word, because the concepts are not fictions, but natural responses to encountering individuals in the world. I am an Ockhamist. |
| 9723 | Sentences with 'if' are only conditionals if they can read as A-implies-B [Enderton] |
| Full Idea: Not all sentences using 'if' are conditionals. Consider 'if you want a banana, there is one in the kitchen'. The rough test is that a conditional can be rewritten as 'that A implies that B'. | |
| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], 1.6.4) |
| 114 | Rhetoric can produce conviction, but not educate people about right and wrong [Plato] |
| Full Idea: Rhetoric is an agent of the kind of persuasion which is designed to produce conviction, but not to educate people about right and wrong. | |
| From: Plato (Gorgias [c.387 BCE], 455a) | |
| A reaction: Surely there must be good rhetoric (or at least it is an open question)? |
| 116 | Rhetoric is irrational about its means and its ends [Plato] |
| Full Idea: Rhetoric is a knack, because it lacks rational understanding of its object or what it dispenses (and can't explain the reason anything happens). | |
| From: Plato (Gorgias [c.387 BCE], 465a) | |
| A reaction: If there are cunning people who have the wrong sort of intelligence for morality, there must be cunning users of rhetoric who know exactly what they are doing. |
| 135 | All activity aims at the good [Plato] |
| Full Idea: All activity aims at the good. | |
| From: Plato (Gorgias [c.387 BCE], 499e) | |
| A reaction: He includes non-conscious activity, so this is the 'teleological' view of nature, which seems a bit optimistic to the modern mind. |
| 122 | Moral rules are made by the weak members of humanity [Plato] |
| Full Idea: Callicles: It's the weaklings who constitute the majority of the human race who make the rules. | |
| From: Plato (Gorgias [c.387 BCE], 483b) | |
| A reaction: An aristocrat bemoans democracy. Presumably the qualification for being a 'weakling' is shortage of money. How strong are the scions of the aristocrats? |
| 139 | A good person is bound to act well, and this brings happiness [Plato] |
| Full Idea: A good person is bound to do whatever he does well and successfully, and success brings fulfilment and happiness. | |
| From: Plato (Gorgias [c.387 BCE], 507c) | |
| A reaction: Not how we would see it, I guess, but this is the Greek idea that a good person is one who functions well. Anyone who functions well is probably having a good time. |
| 128 | Is it natural to simply indulge our selfish desires? [Plato] |
| Full Idea: Callicles: Nature says the only authentic way of life is to do nothing to hinder or restrain the expansion of one's desires. | |
| From: Plato (Gorgias [c.387 BCE], 491e) | |
| A reaction: Sounds like the natural desires of a young single man. Parents and spouses have natural desires that focus on other people's desires. |
| 4322 | In slaking our thirst the goodness of the action and the pleasure are clearly separate [Plato] |
| Full Idea: When we drink to quench thirst, we lose the distress of the thirst and the pleasure of drinking at the same moment, but one loss is good and the other bad, so the pleasure and the goodness must be separate. | |
| From: Plato (Gorgias [c.387 BCE], 497d) | |
| A reaction: This is open to the objection that the good of slaking one's thirst is a long-term pleasure, where the drinking is short-term, so pleasure is still the good. |
| 136 | Good should be the aim of pleasant activity, not the other way round [Plato] |
| Full Idea: Good should be the goal of pleasant activities, rather than pleasure being the goal of good activities. | |
| From: Plato (Gorgias [c.387 BCE], 500a) | |
| A reaction: Nice. Not far off what Aristotle says on the topic. So what activities should we seek out? Narrow the pleasures down to the good ones, or narrow the good ones down to the pleasurable? |
| 134 | Good and bad people seem to experience equal amounts of pleasure and pain [Plato] |
| Full Idea: There is little to tell between good and bad people (e.g. cowards) in terms of how much pleasure and distress they experience. | |
| From: Plato (Gorgias [c.387 BCE], 498c) | |
| A reaction: A very perceptive remark. If the good are people with empathy for others, then they may suffer more distress than the insensitive wicked. |
| 132 | If happiness is the satisfaction of desires, then a life of scratching itches should be happiness [Plato] |
| Full Idea: Socrates: I want to ask whether a lifetime spent scratching, itching and scratching, no end of scratching, is also a life of happiness. | |
| From: Plato (Gorgias [c.387 BCE], 494c) | |
| A reaction: There are plenty of people who think 'fun' is the main aim of life, and who fit what Socrates is referring to. We don't admire such a life, but not many people can be admired. |
| 4319 | In a fool's mind desire is like a leaky jar, insatiable in its desires, and order and contentment are better [Plato] |
| Full Idea: In a fool's mind desire is a leaky jar, …which is an analogy for the mind's insatiability, showing we should prefer an orderly life, in which one is content with whatever is to hand, to a self-indulgent life of insatiable desire. | |
| From: Plato (Gorgias [c.387 BCE], 493b) | |
| A reaction: This points to an interesting paradox, that pleasure requires the misery of desire. And yet absence of desire is like death. An Aristotelian mean, of living according to nature, seems the escape route. |
| 130 | Is the happiest state one of sensual, self-indulgent freedom? [Plato] |
| Full Idea: Callicles: If a person has the means to live a life of sensual, self-indulgent freedom, there's no better or happier state of existence. | |
| From: Plato (Gorgias [c.387 BCE], 492c) |
| 120 | Should we avoid evil because it will bring us bad consequences? [Plato] |
| Full Idea: Socrates: We should avoid doing wrong because of all the bad consequences it will bring us. | |
| From: Plato (Gorgias [c.387 BCE], 480a) |
| 118 | I would rather be a victim of crime than a criminal [Plato] |
| Full Idea: Socrates: If I had to choose between doing wrong and having wrong done to me, I'd prefer the latter to the former. | |
| From: Plato (Gorgias [c.387 BCE], 469c) | |
| A reaction: cf Democritus 68B45 |
| 131 | If absence of desire is happiness, then nothing is happier than a stone or a corpse [Plato] |
| Full Idea: Callicles: If people who need nothing are happy, there would be nothing happier than a stone or a corpse. | |
| From: Plato (Gorgias [c.387 BCE], 492e) | |
| A reaction: We aren't really supposed to approve of Callicles, but to me this is a splendidly crushing western response to many of the ideals found in eastern philosophy. |
| 140 | Self-indulgent desire makes friendship impossible, because it makes a person incapable of co-operation [Plato] |
| Full Idea: Self-indulgent desire makes a person incapable of co-operation, which is a prerequisite of friendship. | |
| From: Plato (Gorgias [c.387 BCE], 507e) |
| 119 | A criminal is worse off if he avoids punishment [Plato] |
| Full Idea: Socrates: A criminal is worse off if he doesn't pay the penalty, and continues to do wrong without getting punished. | |
| From: Plato (Gorgias [c.387 BCE], 472e) |
| 129 | Do most people praise self-discipline and justice because they are too timid to gain their own pleasure? [Plato] |
| Full Idea: Callicles: Why do most people praise self-discipline and justice? Because their own timidity makes them incapable of satisfying their pleasures. | |
| From: Plato (Gorgias [c.387 BCE], 492a) |
| 4320 | The popular view is that health is first, good looks second, and honest wealth third [Plato] |
| Full Idea: I'm sure you know the list of human advantages in the party song: 'The very best is health, Second good looks, and third honest wealth'. | |
| From: Plato (Gorgias [c.387 BCE], 451e) | |
| A reaction: This invites the obvious question of why anyone wants these three things, with the implied answer of 'pleasure'. But we might want them even if we couldn't use them, implying pluralism. |
| 137 | As with other things, a good state is organised and orderly [Plato] |
| Full Idea: As in every case (an artefact, a body, a mind, a creature), a good state is an organised and orderly state. | |
| From: Plato (Gorgias [c.387 BCE], 506e) |
| 141 | A good citizen won't be passive, but will redirect the needs of the state [Plato] |
| Full Idea: The only responsibility of a good member of a community is altering the community's needs rather than going along with them. | |
| From: Plato (Gorgias [c.387 BCE], 517b) |
| 123 | Do most people like equality because they are second-rate? [Plato] |
| Full Idea: Callicles: It's because most people are second-rate that they are happy for things to be distributed equally. | |
| From: Plato (Gorgias [c.387 BCE], 483c) |
| 124 | Does nature imply that it is right for better people to have greater benefits? [Plato] |
| Full Idea: Callicles: We only have to look at nature to find evidence that it is right for better to have a greater share than worse. | |
| From: Plato (Gorgias [c.387 BCE], 483d) |
| 19381 | The past has ceased to exist, and the future does not yet exist, so time does not exist [William of Ockham] |
| Full Idea: Time is composed of non-entities, because it is composed of the past which does not exist now, although it did exist, and of the future, which does not yet exist; therefore time does not exist. | |
| From: William of Ockham (works [1335], 6:496), quoted by Richard T.W. Arthur - Leibniz 7 'Nominalist' | |
| A reaction: I've a lot of sympathy with this! I favour Presentism, so the past is gone and the future is yet to arrive. But we have no coherent concept of a present moment of any duration to contain reality. We are just completely bogglificated by it all. |
| 8010 | William of Ockham is the main spokesman for God's commands being the source of morality [William of Ockham] |
| Full Idea: The most notable philosopher who makes God's commandment the basis of goodness, rather than God's goodness a reason for obeying him, is William of Occam. | |
| From: William of Ockham (works [1335]), quoted by Alasdair MacIntyre - A Short History of Ethics Ch.9 | |
| A reaction: Either view has problems. Why choose God to obey? Obey anyone who is powerful? But how do you decide that God is good? How do we know the nature of God's commands, or the nature of God's goodness? Etc. |
| 16679 | Even an angel must have some location [William of Ockham, by Pasnau] |
| Full Idea: Ockham dismisses the possibility of non-location out of hand, remarking that even an angel has some location. | |
| From: report of William of Ockham (works [1335]) by Robert Pasnau - Metaphysical Themes 1274-1671 14.4 |