36 ideas
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] |
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] |
9476 | If dispositions are more fundamental than causes, then they won't conceptually reduce to them [Bird on Lewis] |
10990 | Conditionals are truth-functional, but unassertable in tricky cases? [Grice, by Read] |
8425 | For true counterfactuals, both antecedent and consequent true is closest to actuality [Lewis] |
8424 | Determinism says there can't be two identical worlds up to a time, with identical laws, which then differ [Lewis] |
8420 | A proposition is a set of possible worlds where it is true [Lewis] |
10991 | Key conversational maxims are 'quality' (assert truth) and 'quantity' (leave nothing out) [Grice, by Read] |
8405 | A theory of causation should explain why cause precedes effect, not take it for granted [Lewis, by Field,H] |
8427 | I reject making the direction of causation axiomatic, since that takes too much for granted [Lewis] |
10392 | It is just individious discrimination to pick out one cause and label it as 'the' cause [Lewis] |
8419 | The modern regularity view says a cause is a member of a minimal set of sufficient conditions [Lewis] |
8421 | Regularity analyses could make c an effect of e, or an epiphenomenon, or inefficacious, or pre-empted [Lewis] |
17525 | The counterfactual view says causes are necessary (rather than sufficient) for their effects [Lewis, by Bird] |
17524 | Lewis has basic causation, counterfactuals, and a general ancestral (thus handling pre-emption) [Lewis, by Bird] |
8397 | Counterfactual causation implies all laws are causal, which they aren't [Tooley on Lewis] |
8423 | My counterfactual analysis applies to particular cases, not generalisations [Lewis] |
8426 | One event causes another iff there is a causal chain from first to second [Lewis] |
4795 | Lewis's account of counterfactuals is fine if we know what a law of nature is, but it won't explain the latter [Cohen,LJ on Lewis] |