39 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] |
18189 | ZFC could contain a contradiction, and it can never prove its own consistency [MacLane] |
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] |
14703 | Superficial necessity is true in all worlds; deep necessity is thus true, no matter which world is actual [Schroeter] |
14714 | Contradictory claims about a necessary god both seem apriori coherent [Schroeter] |
14704 | 2D semantics gives us apriori knowledge of our own meanings [Schroeter] |
14706 | Your view of water depends on whether you start from the actual Earth or its counterfactual Twin [Schroeter] |
14711 | Rationalists say knowing an expression is identifying its extension using an internal cognitive state [Schroeter] |
14717 | Internalist meaning is about understanding; externalist meaning is about embedding in a situation [Schroeter] |
14720 | Semantic theory assigns meanings to expressions, and metasemantics explains how this works [Schroeter] |
14695 | Semantic theories show how truth of sentences depends on rules for interpreting and joining their parts [Schroeter] |
14696 | Simple semantics assigns extensions to names and to predicates [Schroeter] |
14697 | 'Federer' and 'best tennis player' can't mean the same, despite having the same extension [Schroeter] |
14698 | Possible worlds semantics uses 'intensions' - functions which assign extensions at each world [Schroeter] |
14699 | Possible worlds make 'I' and that person's name synonymous, but they have different meanings [Schroeter] |
14709 | Possible worlds semantics implies a constitutive connection between meanings and modal claims [Schroeter] |
14719 | In the possible worlds account all necessary truths are same (because they all map to the True) [Schroeter] |
14701 | Array worlds along the horizontal, and contexts (world,person,time) along the vertical [Schroeter] |
14702 | If we introduce 'actually' into modal talk, we need possible worlds twice to express this [Schroeter] |
14705 | Do we know apriori how we refer to names and natural kinds, but their modal profiles only a posteriori? [Schroeter] |
14715 | 2D fans defend it for conceptual analysis, for meaning, and for internalist reference [Schroeter] |
14716 | 2D semantics can't respond to contingent apriori claims, since there is no single proposition involved [Schroeter] |