121 ideas
5196 | Philosophy is a department of logic [Ayer] |
5189 | Philosophers should abandon speculation, as philosophy is wholly critical [Ayer] |
7919 | Humeans rejected the a priori synthetic, and so rejected even Kantian metaphysics [Ayer, by Macdonald,C] |
5195 | Critics say analysis can only show the parts, and not their distinctive configuration [Ayer] |
5179 | Philosophy deals with the questions that scientists do not wish to handle [Ayer] |
5331 | You can't infer that because you have a hidden birth-mark, everybody else does [Ayer] |
19463 | Induction assumes some uniformity in nature, or that in some respects the future is like the past [Ayer] |
4749 | We cannot analyse the concept of 'truth', because it is simply a mark that a sentence is asserted [Ayer] |
13520 | A 'tautology' must include connectives [Wolf,RS] |
13524 | Deduction Theorem: T∪{P}|-Q, then T|-(P→Q), which justifies Conditional Proof [Wolf,RS] |
13522 | Universal Generalization: If we prove P(x) with no special assumptions, we can conclude ∀xP(x) [Wolf,RS] |
13521 | Universal Specification: ∀xP(x) implies P(t). True for all? Then true for an instance [Wolf,RS] |
13523 | Existential Generalization (or 'proof by example'): if we can say P(t), then we can say something is P [Wolf,RS] |
13529 | Empty Set: ∃x∀y ¬(y∈x). The unique empty set exists [Wolf,RS] |
13526 | Comprehension Axiom: if a collection is clearly specified, it is a set [Wolf,RS] |
13534 | In first-order logic syntactic and semantic consequence (|- and |=) nicely coincide [Wolf,RS] |
13535 | First-order logic is weakly complete (valid sentences are provable); we can't prove every sentence or its negation [Wolf,RS] |
13531 | Model theory reveals the structures of mathematics [Wolf,RS] |
13532 | Model theory 'structures' have a 'universe', some 'relations', some 'functions', and some 'constants' [Wolf,RS] |
13519 | Model theory uses sets to show that mathematical deduction fits mathematical truth [Wolf,RS] |
13533 | First-order model theory rests on completeness, compactness, and the Löwenheim-Skolem-Tarski theorem [Wolf,RS] |
13537 | An 'isomorphism' is a bijection that preserves all structural components [Wolf,RS] |
13539 | The LST Theorem is a serious limitation of first-order logic [Wolf,RS] |
13538 | If a theory is complete, only a more powerful language can strengthen it [Wolf,RS] |
13525 | Most deductive logic (unlike ordinary reasoning) is 'monotonic' - we don't retract after new givens [Wolf,RS] |
1553 | No perceptible object is truly straight or curved [Protagoras] |
13530 | An ordinal is an equivalence class of well-orderings, or a transitive set whose members are transitive [Wolf,RS] |
13518 | Modern mathematics has unified all of its objects within set theory [Wolf,RS] |
5202 | Maths and logic are true universally because they are analytic or tautological [Ayer] |
6523 | Positivists regard ontology as either meaningless or stipulated [Ayer, by Robinson,H] |
2611 | It is currently held that quantifying over something implies belief in its existence [Ayer] |
16520 | We see properties necessary for a kind (in the definition), but not for an individual [Ayer] |
5183 | Only tautologies can be certain; other propositions can only be probable [Ayer] |
19461 | Knowing I exist reveals nothing at all about my nature [Ayer] |
19459 | To say 'I am not thinking' must be false, but it might have been true, so it isn't self-contradictory [Ayer] |
19460 | 'I know I exist' has no counterevidence, so it may be meaningless [Ayer] |
1549 | Everything that exists consists in being perceived [Protagoras] |
6525 | Logical positivists could never give the sense-data equivalent of 'there is a table next door' [Robinson,H on Ayer] |
5170 | Material things are constructions from actual and possible occurrences of sense-contents [Ayer] |
8824 | No one has defended translational phenomenalism since Ayer in 1940 [Ayer, by Kim] |
2614 | Modern phenomenalism holds that objects are logical constructions out of sense-data [Ayer] |
5198 | We could verify 'a thing can't be in two places at once' by destroying one of the things [Ierubino on Ayer] |
2619 | Whether geometry can be applied to reality is an empirical question outside of geometry [Ayer] |
5197 | By changing definitions we could make 'a thing can't be in two places at once' a contradiction [Ayer] |
5204 | To say that a proposition is true a priori is to say that it is a tautology [Ayer] |
2615 | The concept of sense-data allows us to discuss appearances without worrying about reality [Ayer] |
6524 | Positivists prefer sense-data to objects, because the vocabulary covers both illusions and perceptions [Ayer, by Robinson,H] |
5193 | Causal and representative theories of perception are wrong as they refer to unobservables [Ayer] |
5200 | The main claim of rationalism is that thought is an independent source of knowledge [Ayer] |
4729 | Empiricism lacked a decent account of the a priori, until Ayer said it was entirely analytic [O'Grady on Ayer] |
5180 | All propositions (especially 'metaphysics') must begin with the senses [Ayer] |
5169 | My empiricism logically distinguishes analytic and synthetic propositions, and metaphysical verbiage [Ayer] |
5185 | It is further sense-experience which informs us of the mistakes that arise out of sense-experience [Ayer] |
5199 | Empiricism, it is said, cannot account for our knowledge of necessary truths [Ayer] |
5163 | Basic propositions refer to a single experience, are incorrigible, and conclusively verifiable [Ayer] |
1545 | Protagoras was the first to claim that there are two contradictory arguments about everything [Protagoras, by Diog. Laertius] |
1547 | Man is the measure of all things - of things that are, and of things that are not [Protagoras] |
3305 | There is no more purely metaphysical doctrine than Protagorean relativism [Benardete,JA on Protagoras] |
3317 | You can only state the problem of the relative warmth of an object by agreeing on the underlying object [Benardete,JA on Protagoras] |
3313 | If my hot wind is your cold wind, then wind is neither hot nor cold, and so not as cold as itself [Benardete,JA on Protagoras] |
247 | God is "the measure of all things", more than any man [Plato on Protagoras] |
606 | Protagoras absurdly thought that the knowing or perceiving man is 'the measure of all things' [Aristotle on Protagoras] |
612 | Relativists think if you poke your eye and see double, there must be two things [Aristotle on Protagoras] |
19464 | We only discard a hypothesis after one failure if it appears likely to keep on failing [Ayer] |
5190 | The induction problem is to prove generalisations about the future based on the past [Ayer] |
19462 | Induction passes from particular facts to other particulars, or to general laws, non-deductively [Ayer] |
5191 | We can't use the uniformity of nature to prove induction, as that would be circular [Ayer] |
5177 | Other minds are 'metaphysical' objects, because I can never observe their experiences [Ayer] |
5662 | Maybe induction could never prove the existence of something unobservable [Ayer] |
5178 | A conscious object is by definition one that behaves in a certain way, so behaviour proves consciousness [Ayer] |
5167 | The argument from analogy fails, so the best account of other minds is behaviouristic [Ayer] |
2613 | The theory of other minds has no rival [Ayer] |
5328 | Originally I combined a mentalistic view of introspection with a behaviouristic view of other minds [Ayer] |
5330 | Physicalism undercuts the other mind problem, by equating experience with 'public' brain events [Ayer] |
5664 | Consciousness must involve a subject, and only bodies identify subjects [Ayer] |
5172 | If the self is meaningful, it must be constructed from sense-experiences [Ayer] |
5326 | Qualia must be united by a subject, because they lead to concepts and judgements [Ayer] |
5325 | Is something an 'experience' because it relates to other experiences, or because it relates to a subject? [Ayer] |
5324 | Bodily identity and memory work together to establish personal identity [Ayer] |
5173 | Two experiences belong to one self if their contents belong with one body [Ayer] |
5176 | Empiricists can define personal identity as bodily identity, which consists of sense-contents [Ayer] |
5668 | People own conscious states because they are causally related to the identifying body [Ayer] |
5322 | Self-consciousness is not basic, because experiences are not instrinsically marked with ownership [Ayer] |
5661 | We identify experiences by their owners, so we can't define owners by their experiences [Ayer] |
5665 | Memory is the best proposal as what unites bundles of experiences [Ayer] |
5666 | Not all exerience can be remembered, as this would produce an infinite regress [Ayer] |
5327 | Temporal gaps in the consciousness of a spirit could not be bridged by memories [Ayer] |
5669 | Personal identity can't just be relations of experiences, because the body is needed to identify them [Ayer] |
5171 | The supposed 'gulf' between mind and matter is based on the senseless concept of 'substances' [Ayer] |
5329 | Why shouldn't we say brain depends on mind? Better explanation! [Ayer] |
5181 | A sentence is factually significant to someone if they know how to verify its proposition [Ayer] |
5184 | Factual propositions imply (in conjunction with a few other premises) possible experiences [Ayer] |
5186 | Tautologies and empirical hypotheses form the entire class of significant propositions [Ayer] |
5164 | A statement is meaningful if observation statements can be deduced from it [Ayer] |
5165 | Directly verifiable statements must entail at least one new observation statement [Ayer] |
5166 | The principle of verification is not an empirical hypothesis, but a definition [Ayer] |
5162 | Sentences only express propositions if they are meaningful; otherwise they are 'statements' [Ayer] |
2610 | Talk of propositions is just shorthand for talking about equivalent sentences [Ayer] |
6968 | Some people think there are ethical facts, but of a 'queer' sort [Ayer] |
6972 | A right attitude is just an attitude one is prepared to stand by [Ayer] |
6973 | Moral theories are all meta-ethical, and are neutral as regards actual conduct [Ayer] |
6974 | Moral judgements cannot be the logical consequence of a moral philosophy [Ayer] |
5205 | Moral intuition is worthless if there is no criterion to decide between intuitions [Ayer] |
6971 | I would describe intuitions of good as feelings of approval [Ayer] |
23725 | Ayer defends the emotivist version of expressivism [Ayer, by Smith,M] |
5206 | To say an act is wrong makes no further statement about it, but merely expresses disapproval [Ayer] |
6969 | Approval of historical or fictional murders gives us leave to imitate them [Ayer] |
6970 | Moral judgements are not expressions, but are elements in a behaviour pattern [Ayer] |
5168 | Moral approval and disapproval concerns classes of actions, rather than particular actions [Ayer] |
6016 | Early sophists thought convention improved nature; later they said nature was diminished by it [Protagoras, by Miller,FD] |
1580 | For Protagoras the only bad behaviour is that which interferes with social harmony [Protagoras, by Roochnik] |
205 | Protagoras contradicts himself by saying virtue is teachable, but then that it is not knowledge [Plato on Protagoras] |
1659 | Protagoras seems to have made the huge move of separating punishment from revenge [Protagoras, by Vlastos] |
532 | Successful education must go deep into the soul [Protagoras] |
1552 | He spent public money on education, as it benefits the individual and the state [Protagoras, by Diodorus of Sicily] |
15251 | The attribution of necessity to causation is either primitive animism, or confusion with logical necessity [Ayer] |
5208 | A person with non-empirical attributes is unintelligible. [Ayer] |
5187 | When we ascribe an attribute to a thing, we covertly assert that it exists [Ayer] |
5207 | If theism is non-sensical, then so is atheism. [Ayer] |
1551 | He said he didn't know whether there are gods - but this is the same as atheism [Diogenes of Oen. on Protagoras] |
5209 | The 'truths' expressed by theists are not literally significant [Ayer] |