40 ideas
| 16943 | Philosophy is continuous with science, and has no external vantage point [Quine] |
| 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] |
| 16949 | Klein summarised geometry as grouped together by transformations [Quine] |
| 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] |
| 16939 | Mass terms just concern spread, but other terms involve both spread and individuation [Quine] |
| 16948 | Once we know the mechanism of a disposition, we can eliminate 'similarity' [Quine] |
| 16945 | We judge things to be soluble if they are the same kind as, or similar to, things that do dissolve [Quine] |
| 2614 | Modern phenomenalism holds that objects are logical constructions out of sense-data [Ayer] |
| 2615 | The concept of sense-data allows us to discuss appearances without worrying about reality [Ayer] |
| 16944 | Science is common sense, with a sophisticated method [Quine] |
| 16940 | Induction is just more of the same: animal expectations [Quine] |
| 16941 | Induction relies on similar effects following from each cause [Quine] |
| 16933 | Grue is a puzzle because the notions of similarity and kind are dubious in science [Quine] |
| 16934 | General terms depend on similarities among things [Quine] |
| 16938 | To learn yellow by observation, must we be told to look at the colour? [Quine] |
| 8486 | Standards of similarity are innate, and the spacing of qualities such as colours can be mapped [Quine] |
| 16947 | Similarity is just interchangeability in the cosmic machine [Quine] |
| 16932 | Projectible predicates can be universalised about the kind to which they refer [Quine] |
| 7375 | Quine probably regrets natural kinds now being treated as essences [Quine, by Dennett] |
| 16935 | If similarity has no degrees, kinds cannot be contained within one another [Quine] |
| 16936 | Comparative similarity allows the kind 'colored' to contain the kind 'red' [Quine] |
| 16937 | You can't base kinds just on resemblance, because chains of resemblance are a muddle [Quine] |
| 16942 | It is hard to see how regularities could be explained [Quine] |