53 ideas
| 9247 | Life will be lived better if it has no meaning [Camus] |
| Full Idea: Life will be lived all the better if it has no meaning. | |
| From: Albert Camus (The Myth of Sisyphus [1942], 'Abs free') | |
| A reaction: One image of the good life is that of a successful wild animal, for which existence is not a problem, merely a constant activity and pursuit. Maybe life begins to acquire meaning once we realise that meaning should not be sought directly. |
| 6707 | Suicide - whether life is worth living - is the one serious philosophical problem [Camus] |
| Full Idea: There is but one truly serious philosophical problem and that is suicide. Judgine whether life is or is not worth living amounts to answering the fundamental question of philosophy. | |
| From: Albert Camus (The Myth of Sisyphus [1942], p.11) | |
| A reaction: What a wonderful thesis for a book. In Idea 2682 there is the possibility of life being worth living, but not worth a huge amount of effort. It is better to call Camus' question the first question, rather than the only question. |
| 9245 | To an absurd mind reason is useless, and there is nothing beyond reason [Camus] |
| Full Idea: To an absurd mind reason is useless, and there is nothing beyond reason. | |
| From: Albert Camus (The Myth of Sisyphus [1942], 'Phil Suic') | |
| A reaction: But there is, surely, intuition and instinct? Read Keats's Letters. There is good living through upbringing and habit. Read Aristotle. If you like Camus' thought, you will love Chuang Tzu. Personally I am a child of the Enlightenment. |
| 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] |
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Full Idea:
F(x) is a 'function', which indicates the unique value which y takes in |
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| From: Herbert B. Enderton (A Mathematical Introduction to Logic (2nd) [2001], Ch.0) |
| 13201 | ∈ says the whole set is in the other; ⊆ says the members of the subset are in the other [Enderton] |
| Full Idea: To know if A ∈ B, we look at the set A as a single object, and check if it is among B's members. But if we want to know whether A ⊆ B then we must open up set A and check whether its various members are among the members of B. | |
| From: Herbert B. Enderton (Elements of Set Theory [1977], 1:04) | |
| A reaction: This idea is one of the key ideas to grasp if you are going to get the hang of set theory. John ∈ USA ∈ UN, but John is not a member of the UN, because he isn't a country. See Idea 12337 for a special case. |
| 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) |
| 13204 | The 'ordered pair' <x,y> is defined to be {{x}, {x,y}} [Enderton] |
| Full Idea: The 'ordered pair' <x,y> is defined to be {{x}, {x,y}}; hence it can be proved that <u,v> = <x,y> iff u = x and v = y (given by Kuratowski in 1921). ...The definition is somewhat arbitrary, and others could be used. | |
| From: Herbert B. Enderton (Elements of Set Theory [1977], 3:36) | |
| A reaction: This looks to me like one of those regular cases where the formal definitions capture all the logical behaviour of the concept that are required for inference, while failing to fully capture the concept for ordinary conversation. |
| 13206 | A 'linear or total ordering' must be transitive and satisfy trichotomy [Enderton] |
| Full Idea: A 'linear ordering' (or 'total ordering') on A is a binary relation R meeting two conditions: R is transitive (of xRy and yRz, the xRz), and R satisfies trichotomy (either xRy or x=y or yRx). | |
| From: Herbert B. Enderton (Elements of Set Theory [1977], 3:62) |
| 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) |
| 13200 | Note that {Φ} =/= Φ, because Φ ∈ {Φ} but Φ ∉ Φ [Enderton] |
| Full Idea: Note that {Φ} =/= Φ, because Φ ∈ {Φ} but Φ ∉ Φ. A man with an empty container is better off than a man with nothing. | |
| From: Herbert B. Enderton (Elements of Set Theory [1977], 1.03) |
| 13199 | The empty set may look pointless, but many sets can be constructed from it [Enderton] |
| Full Idea: It might be thought at first that the empty set would be a rather useless or even frivolous set to mention, but from the empty set by various set-theoretic operations a surprising array of sets will be constructed. | |
| From: Herbert B. Enderton (Elements of Set Theory [1977], 1:02) | |
| A reaction: This nicely sums up the ontological commitments of mathematics - that we will accept absolutely anything, as long as we can have some fun with it. Sets are an abstraction from reality, and the empty set is the very idea of that abstraction. |
| 13203 | The singleton is defined using the pairing axiom (as {x,x}) [Enderton] |
| Full Idea: Given any x we have the singleton {x}, which is defined by the pairing axiom to be {x,x}. | |
| From: Herbert B. Enderton (Elements of Set Theory [1977], 2:19) | |
| A reaction: An interesting contrivance which is obviously aimed at keeping the axioms to a minimum. If you can do it intuitively with a new axiom, or unintuitively with an existing axiom - prefer the latter! |
| 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) |
| 13202 | Fraenkel added Replacement, to give a theory of ordinal numbers [Enderton] |
| Full Idea: It was observed by several people that for a satisfactory theory of ordinal numbers, Zermelo's axioms required strengthening. The Axiom of Replacement was proposed by Fraenkel and others, giving rise to the Zermelo-Fraenkel (ZF) axioms. | |
| From: Herbert B. Enderton (Elements of Set Theory [1977], 1:15) |
| 13205 | We can only define functions if Choice tells us which items are involved [Enderton] |
| Full Idea: For functions, we know that for any y there exists an appropriate x, but we can't yet form a function H, as we have no way of defining one particular choice of x. Hence we need the axiom of choice. | |
| From: Herbert B. Enderton (Elements of Set Theory [1977], 3:48) |
| 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) |
| 9244 | Logic is easy, but what about logic to the point of death? [Camus] |
| Full Idea: It is always easy to be logical. It is almost impossible to be logical to the bitter end. The only problem that interests me is: is there a logic to the point of death? | |
| From: Albert Camus (The Myth of Sisyphus [1942], 'Abs and Suic') | |
| A reaction: This is a lovely hand grenade to lob into an analytical logic class! It is very hard to get logicians to actually ascribe a clear value to their activity. They tend to present it as a marginal private game, and yet it has high status. |
| 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. |
| 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) |
| 9249 | Whether we are free is uninteresting; we can only experience our freedom [Camus] |
| Full Idea: Knowing whether or not a man is free doesn't interest me. I can only experience my own freedom. | |
| From: Albert Camus (The Myth of Sisyphus [1942], 'Abs free') | |
| A reaction: Camus has the right idea. Personally I think you could drop the word 'freedom', and just say that I am confronted by the need to make decisions. |
| 9253 | The human heart has a tiresome tendency to label as fate only what crushes it [Camus] |
| Full Idea: The human heart has a tiresome tendency to label as fate only what crushes it. | |
| From: Albert Camus (The Myth of Sisyphus [1942], 'Appendix') | |
| A reaction: Nice. It might just as much be fate that you live a happy bourgeois life, as that you inadvertently murder your own father at a crossroads. But you can't avoid the powerful awareness of fate when a road accident occurs. |
| 9250 | Discussing ethics is pointless; moral people behave badly, and integrity doesn't need rules [Camus] |
| Full Idea: There can be no question of holding forth on ethics. I have seen people behave badly with great morality and I note every day that integrity has no need of rules. | |
| From: Albert Camus (The Myth of Sisyphus [1942], 'Abs Man') | |
| A reaction: I don't agree. If someone 'behaves badly with great morality' there is something wrong with their morality, and I want to know what it is. The last part is more plausible, and could be a motto for Particularism. Rules dangerously over-simplify life. |
| 9252 | The more one loves the stronger the absurd grows [Camus] |
| Full Idea: The more one loves the stronger the absurd grows. | |
| From: Albert Camus (The Myth of Sisyphus [1942], 'Don Juan') | |
| A reaction: A penetrating remark, to be placed as a contrary to the remarks of Harry Frankfurt on love. But if the absurd increases the intensity of life, as Camus thinks, then they both make love the great life-affirmation, but in different ways. |
| 5954 | All inventions of the mind aim at pleasure, and those that don't are worthless [Metrodorus of Lamp., by Plutarch] |
| Full Idea: Metrodorus says that all the wonderful, ingenious and brilliant inventions of the mind have been contrived for the sake of pleasure of the flesh or for the sake of looking forward to it, and any accomplishment not leading to this end is worthless. | |
| From: report of Metrodorus (Lamp) (fragments/reports [c.291 BCE], Fr 6) by Plutarch - 74: Reply to Colotes §1125 | |
| A reaction: It is very hard to think of counterexamples! Would anyone bother to work out the theorems of number theory if they didn't enjoy doing it? Would any sensible person make great sacrifices if they didn't think that increased happiness would result? |
| 9251 | One can be virtuous through a whim [Camus] |
| Full Idea: One can be virtuous through a whim. | |
| From: Albert Camus (The Myth of Sisyphus [1942], 'Abs Man') | |
| A reaction: A nice remark. Obviously neither Aristotle nor Kant would be too impressed by someone who did this, and Aristotle would certainly say that it is not really virtue, but merely right behaviour. I agree with Aristotle. |
| 9243 | If we believe existence is absurd, this should dictate our conduct [Camus] |
| Full Idea: What a man believes to be true must determine his action. Belief in the absurdity of existence must then dictate his conduct. | |
| From: Albert Camus (The Myth of Sisyphus [1942], 'Abs and Suic') | |
| A reaction: It is intriguing to speculate what the appropriate conduct is. Presumably it is wild existential gestures, like sticking a knife through your hand. Suicide will be an obvious temptation. But bourgeois life might be equally appropriate. |
| 6708 | Happiness and the absurd go together, each leading to the other [Camus] |
| Full Idea: Happiness and the absurd are two sons of the same earth; they are inseparable; it would be a mistake to say that happiness necessarily springs from the absurd discovery; it happens as well that the feeling of the absurd springs from happiness. | |
| From: Albert Camus (The Myth of Sisyphus [1942], p.110) | |
| A reaction: I'm not sure that I understand this, but I understand the experience of absurdity, and I can see that somehow one feels a bit more alive when one acknowledges the absurdity of it all. Meta-meta-thought is the highest form of human life, I say. |
| 9242 | Essential problems either risk death, or intensify the passion of life [Camus] |
| Full Idea: The essential problems are those that run the risk of leading to death, or those that intensify the passion of living. | |
| From: Albert Camus (The Myth of Sisyphus [1942], 'Abs and Suic') | |
| A reaction: This seems to be distinctively existentialist, in a way that a cool concern for great truths are not ranked as so important. Ranking dangerous problems as crucial seems somehow trivial for a philosopher. Intensity of life is more impressive. |
| 9246 | Danger and integrity are not in the leap of faith, but in remaining poised just before the leap [Camus] |
| Full Idea: The leap of faith does not represent an extreme danger as Kierkegaard would like it to do. The danger, on the contrary, lies in the subtle instant that precedes the leap. Being able to remain on the dizzying crest - that is integrity. | |
| From: Albert Camus (The Myth of Sisyphus [1942], 'Phil Suic') | |
| A reaction: I have always found that a thrilling thought. It perfectly distinguishes atheist existentialism from religious existentialism. It is Camus' best image for how the Absurd can be a life affirming idea, rather than a sort of nihilism. Life gains intensity. |
| 9248 | It is essential to die unreconciled and not of one's own free will [Camus] |
| Full Idea: It is essential to die unreconciled and not of one's own free will. Suicide is a repudiation. | |
| From: Albert Camus (The Myth of Sisyphus [1942], 'Abs free') | |
| A reaction: Camus' whole book addresses the question of suicide. He suggests that life can be redeemed and become livable if you squarely face up to the absurdity of it, and the gap between what we hope for and what we get. |