73 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] |
15413 | With four tense operators, all complex tenses reduce to fourteen basic cases [Burgess] |
15415 | The temporal Barcan formulas fix what exists, which seems absurd [Burgess] |
15430 | Is classical logic a part of intuitionist logic, or vice versa? [Burgess] |
15431 | It is still unsettled whether standard intuitionist logic is complete [Burgess] |
21602 | Many-valued logics don't solve vagueness; its presence at the meta-level is ignored [Williamson] |
15429 | Relevance logic's → is perhaps expressible by 'if A, then B, for that reason' [Burgess] |
11211 | If a sound conclusion comes from two errors that cancel out, the path of the argument must matter [Rumfitt] |
15404 | Technical people see logic as any formal system that can be studied, not a study of argument validity [Burgess] |
15405 | Classical logic neglects the non-mathematical, such as temporality or modality [Burgess] |
15427 | The Cut Rule expresses the classical idea that entailment is transitive [Burgess] |
15421 | Classical logic neglects counterfactuals, temporality and modality, because maths doesn't use them [Burgess] |
15403 | Philosophical logic is a branch of logic, and is now centred in computer science [Burgess] |
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] |
15407 | Formalising arguments favours lots of connectives; proving things favours having very few [Burgess] |
11212 | The sense of a connective comes from primitively obvious rules of inference [Rumfitt] |
11210 | Standardly 'and' and 'but' are held to have the same sense by having the same truth table [Rumfitt] |
15424 | Asserting a disjunction from one disjunct seems odd, but can be sensible, and needed in maths [Burgess] |
15409 | All occurrences of variables in atomic formulas are free [Burgess] |
15414 | The denotation of a definite description is flexible, rather than rigid [Burgess] |
15406 | 'Induction' and 'recursion' on complexity prove by connecting a formula to its atomic components [Burgess] |
21612 | Or-elimination is 'Argument by Cases'; it shows how to derive C from 'A or B' [Williamson] |
15426 | We can build one expanding sequence, instead of a chain of deductions [Burgess] |
15425 | The sequent calculus makes it possible to have proof without transitivity of entailment [Burgess] |
15408 | 'Tautologies' are valid formulas of classical sentential logic - or substitution instances in other logics [Burgess] |
15418 | Validity (for truth) and demonstrability (for proof) have correlates in satisfiability and consistency [Burgess] |
15412 | Models leave out meaning, and just focus on truth values [Burgess] |
15411 | We only need to study mathematical models, since all other models are isomorphic to these [Burgess] |
15416 | We aim to get the technical notion of truth in all models matching intuitive truth in all instances [Burgess] |
15428 | The Liar seems like a truth-value 'gap', but dialethists see it as a 'glut' [Burgess] |
21599 | A sorites stops when it collides with an opposite sorites [Williamson] |
21589 | When bivalence is rejected because of vagueness, we lose classical logic [Williamson] |
21596 | Vagueness undermines the stable references needed by 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] |
15420 | De re modality seems to apply to objects a concept intended for sentences [Burgess] |
15419 | General consensus is S5 for logical modality of validity, and S4 for proof [Burgess] |
15417 | Logical necessity has two sides - validity and demonstrability - which coincide in classical logic [Burgess] |
15422 | Three conditionals theories: Materialism (material conditional), Idealism (true=assertable), Nihilism (no truth) [Burgess] |
15423 | It is doubtful whether the negation of a conditional has any clear meaning [Burgess] |
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] |
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] |
11214 | We learn 'not' along with affirmation, by learning to either affirm or deny a sentence [Rumfitt] |