63 ideas
| 21616 | Truth and falsity apply to suppositions as well as to assertions [Williamson] |
| 21623 | True and false are not symmetrical; false is more complex, involving negation [Williamson] |
| 17925 | Showing a disproof is impossible is not a proof, so don't eliminate double negation [Colyvan] |
| 17926 | Rejecting double negation elimination undermines reductio proofs [Colyvan] |
| 21602 | Many-valued logics don't solve vagueness; its presence at the meta-level is ignored [Williamson] |
| 21611 | Formal semantics defines validity as truth preserved in every model [Williamson] |
| 21606 | 'Bivalence' is the meta-linguistic principle that 'A' in the object language is true or false [Williamson] |
| 21605 | Excluded Middle is 'A or not A' in the object language [Williamson] |
| 17924 | Excluded middle says P or not-P; bivalence says P is either true or false [Colyvan] |
| 17743 | De Morgan introduced a 'universe of discourse', to replace Boole's universe of 'all things' [De Morgan, by Walicki] |
| 21612 | Or-elimination is 'Argument by Cases'; it shows how to derive C from 'A or B' [Williamson] |
| 17929 | Löwenheim proved his result for a first-order sentence, and Skolem generalised it [Colyvan] |
| 17930 | Axioms are 'categorical' if all of their models are isomorphic [Colyvan] |
| 21599 | A sorites stops when it collides with an opposite sorites [Williamson] |
| 17928 | Ordinal numbers represent order relations [Colyvan] |
| 17923 | Intuitionists only accept a few safe infinities [Colyvan] |
| 17941 | Infinitesimals were sometimes zero, and sometimes close to zero [Colyvan] |
| 17922 | Reducing real numbers to rationals suggested arithmetic as the foundation of maths [Colyvan] |
| 17936 | Transfinite induction moves from all cases, up to the limit ordinal [Colyvan] |
| 17940 | Most mathematical proofs are using set theory, but without saying so [Colyvan] |
| 17931 | Structuralism say only 'up to isomorphism' matters because that is all there is to it [Colyvan] |
| 17932 | If 'in re' structures relies on the world, does the world contain rich enough structures? [Colyvan] |
| 21596 | Vagueness undermines the stable references needed by logic [Williamson] |
| 21589 | When bivalence is rejected because of vagueness, we lose classical logic [Williamson] |
| 21601 | A vague term can refer to very precise elements [Williamson] |
| 21629 | Equally fuzzy objects can be identical, so fuzziness doesn't entail vagueness [Williamson] |
| 21591 | Vagueness is epistemic. Statements are true or false, but we often don't know which [Williamson] |
| 21619 | If a heap has a real boundary, omniscient speakers would agree where it is [Williamson] |
| 21620 | The epistemic view says that the essence of vagueness is ignorance [Williamson] |
| 21622 | If there is a true borderline of which we are ignorant, this drives a wedge between meaning and use [Williamson] |
| 9120 | Vagueness in a concept is its indiscriminability from other possible concepts [Williamson] |
| 21625 | The vagueness of 'heap' can remain even when the context is fixed [Williamson] |
| 21614 | The 'nihilist' view of vagueness says that 'heap' is not a legitimate concept [Williamson] |
| 21617 | We can say propositions are bivalent, but vague utterances don't express a proposition [Williamson] |
| 21618 | If the vague 'TW is thin' says nothing, what does 'TW is thin if his perfect twin is thin' say? [Williamson] |
| 21590 | Asking when someone is 'clearly' old is higher-order vagueness [Williamson] |
| 21592 | Supervaluation keeps classical logic, but changes the truth in classical semantics [Williamson] |
| 21603 | You can't give a precise description of a language which is intrinsically vague [Williamson] |
| 21604 | Supervaluation assigns truth when all the facts are respected [Williamson] |
| 21607 | Supervaluation has excluded middle but not bivalence; 'A or not-A' is true, even when A is undecided [Williamson] |
| 21608 | Truth-functionality for compound statements fails in supervaluation [Williamson] |
| 21609 | Supervaluationism defines 'supertruth', but neglects it when defining 'valid' [Williamson] |
| 21610 | Supervaluation adds a 'definitely' operator to classical logic [Williamson] |
| 21613 | Supervaluationism cannot eliminate higher-order vagueness [Williamson] |
| 21633 | Nominalists suspect that properties etc are our projections, and could have been different [Williamson] |
| 21630 | If fuzzy edges are fine, then why not fuzzy temporal, modal or mereological boundaries? [Williamson] |
| 21632 | A river is not just event; it needs actual and counterfactual boundaries [Williamson] |
| 21621 | We can't infer metaphysical necessities to be a priori knowable - or indeed knowable in any way [Williamson] |
| 21627 | We have inexact knowledge when we include margins of error [Williamson] |
| 21626 | Knowing you know (KK) is usually denied if the knowledge concept is missing, or not considered [Williamson] |
| 17943 | Probability supports Bayesianism better as degrees of belief than as ratios of frequencies [Colyvan] |
| 17939 | Mathematics can reveal structural similarities in diverse systems [Colyvan] |
| 17938 | Mathematics can show why some surprising events have to occur [Colyvan] |
| 17934 | Proof by cases (by 'exhaustion') is said to be unexplanatory [Colyvan] |
| 17933 | Reductio proofs do not seem to be very explanatory [Colyvan] |
| 17935 | If inductive proofs hold because of the structure of natural numbers, they may explain theorems [Colyvan] |
| 17942 | Can a proof that no one understands (of the four-colour theorem) really be a proof? [Colyvan] |
| 17937 | Mathematical generalisation is by extending a system, or by abstracting away from it [Colyvan] |
| 21631 | To know, believe, hope or fear, one must grasp the thought, but not when you fail to do them [Williamson] |
| 21600 | 'Blue' is not a family resemblance, because all the blues resemble in some respect [Williamson] |
| 21615 | References to the 'greatest prime number' have no reference, but are meaningful [Williamson] |
| 18038 | The 't' and 'f' of formal semantics has no philosophical interest, and may not refer to true and false [Williamson] |
| 21624 | It is known that there is a cognitive loss in identifying propositions with possible worlds [Williamson] |