43 ideas
| 21584 | A sense of timelessness is essential to wisdom [Russell] |
| 21572 | Philosophical disputes are mostly hopeless, because philosophers don't understand each other [Russell] |
| 21571 | Philosophical systems are interesting, but we now need a more objective scientific philosophy [Russell] |
| 21574 | Hegel's confusions over 'is' show how vast systems can be built on simple errors [Russell] |
| 21587 | Philosophers sometimes neglect truth and distort facts to attain a nice system [Russell] |
| 21582 | Physicists accept particles, points and instants, while pretending they don't do metaphysics [Russell] |
| 21573 | When problems are analysed properly, they are either logical, or not philosophical at all [Russell] |
| 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] |
| 21588 | Logic gives the method of research in philosophy [Russell] |
| 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] |
| 21586 | The logical connectives are not objects, but are formal, and need a context [Russell] |
| 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] |
| 21585 | The tortoise won't win, because infinite instants don't compose an infinitely long time [Russell] |
| 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] |
| 21684 | Atomic facts may be inferrable from others, but never from non-atomic facts [Russell] |
| 22316 | A positive and negative fact have the same constituents; their difference is primitive [Russell] |
| 21576 | With asymmetrical relations (before/after) the reduction to properties is impossible [Russell] |
| 21575 | When we attribute a common quality to a group, we can forget the quality and just talk of the group [Russell] |
| 21580 | Science condemns sense-data and accepts matter, but a logical construction must link them [Russell] |
| 21583 | When sense-data change, there must be indistinguishable sense-data in the process [Russell] |
| 21577 | Empirical truths are particular, so general truths need an a priori input of generality [Russell] |
| 21579 | Objects are treated as real when they connect with other experiences in a normal way [Russell] |
| 21578 | Global scepticism is irrefutable, but can't replace our other beliefs, and just makes us hesitate [Russell] |
| 6416 | Other minds seem to exist, because their testimony supports realism about the world [Russell, by Grayling] |
| 5049 | Intelligent pleasure is the perception of beauty, order and perfection [Leibniz] |
| 21581 | We never experience times, but only succession of events [Russell] |
| 5048 | Perfection is simply quantity of reality [Leibniz] |
| 5050 | Evil serves a greater good, and pain is necessary for higher pleasure [Leibniz] |