179 ideas
18559 | Philosophy is empty if it does not in some way depend on matters of fact [Machery] |
18137 | Impredicative definitions are wrong, because they change the set that is being defined? [Bostock] |
13439 | Venn Diagrams map three predicates into eight compartments, then look for the conclusion [Bostock] |
13421 | 'Disjunctive Normal Form' is ensuring that no conjunction has a disjunction within its scope [Bostock] |
13422 | 'Conjunctive Normal Form' is ensuring that no disjunction has a conjunction within its scope [Bostock] |
13355 | 'Disjunction' says that Γ,φ∨ψ|= iff Γ,φ|= and Γ,ψ|= [Bostock] |
13350 | 'Assumptions' says that a formula entails itself (φ|=φ) [Bostock] |
13351 | 'Thinning' allows that if premisses entail a conclusion, then adding further premisses makes no difference [Bostock] |
13356 | The 'conditional' is that Γ|=φ→ψ iff Γ,φ|=ψ [Bostock] |
13352 | 'Cutting' allows that if x is proved, and adding y then proves z, you can go straight to z [Bostock] |
13353 | 'Negation' says that Γ,¬φ|= iff Γ|=φ [Bostock] |
13354 | 'Conjunction' says that Γ|=φ∧ψ iff Γ|=φ and Γ|=ψ [Bostock] |
13610 | A logic with ¬ and → needs three axiom-schemas and one rule as foundation [Bostock] |
14970 | Normal system K has five axioms and rules [Cresswell] |
14971 | D is valid on every serial frame, but not where there are dead ends [Cresswell] |
14972 | S4 has 14 modalities, and always reduces to a maximum of three modal operators [Cresswell] |
14973 | In S5 all the long complex modalities reduce to just three, and their negations [Cresswell] |
14976 | Reject the Barcan if quantifiers are confined to worlds, and different things exist in other worlds [Cresswell] |
18122 | Classical interdefinitions of logical constants and quantifiers is impossible in intuitionism [Bostock] |
13846 | A 'free' logic can have empty names, and a 'universally free' logic can have empty domains [Bostock] |
18114 | There is no single agreed structure for set theory [Bostock] |
18107 | A 'proper class' cannot be a member of anything [Bostock] |
18115 | We could add axioms to make sets either as small or as large as possible [Bostock] |
18139 | The Axiom of Choice relies on reference to sets that we are unable to describe [Bostock] |
18105 | Replacement enforces a 'limitation of size' test for the existence of sets [Bostock] |
18108 | First-order logic is not decidable: there is no test of whether any formula is valid [Bostock] |
18109 | The completeness of first-order logic implies its compactness [Bostock] |
13346 | Truth is the basic notion in classical logic [Bostock] |
13545 | Elementary logic cannot distinguish clearly between the finite and the infinite [Bostock] |
13822 | Fictional characters wreck elementary logic, as they have contradictions and no excluded middle [Bostock] |
13623 | The syntactic turnstile |- φ means 'there is a proof of φ' or 'φ is a theorem' [Bostock] |
13347 | Validity is a conclusion following for premises, even if there is no proof [Bostock] |
13348 | It seems more natural to express |= as 'therefore', rather than 'entails' [Bostock] |
13349 | Γ|=φ is 'entails'; Γ|= is 'is inconsistent'; |=φ is 'valid' [Bostock] |
13614 | MPP: 'If Γ|=φ and Γ|=φ→ψ then Γ|=ψ' (omit Γs for Detachment) [Bostock] |
13617 | MPP is a converse of Deduction: If Γ |- φ→ψ then Γ,φ|-ψ [Bostock] |
13799 | The sign '=' is a two-place predicate expressing that 'a is the same thing as b' (a=b) [Bostock] |
13800 | |= α=α and α=β |= φ(α/ξ ↔ φ(β/ξ) fix identity [Bostock] |
13803 | If we are to express that there at least two things, we need identity [Bostock] |
13357 | Truth-functors are usually held to be defined by their truth-tables [Bostock] |
13812 | A 'zero-place' function just has a single value, so it is a name [Bostock] |
13811 | A 'total' function ranges over the whole domain, a 'partial' function over appropriate inputs [Bostock] |
13360 | In logic, a name is just any expression which refers to a particular single object [Bostock] |
13361 | An expression is only a name if it succeeds in referring to a real object [Bostock] |
13814 | Definite desciptions resemble names, but can't actually be names, if they don't always refer [Bostock] |
13816 | Because of scope problems, definite descriptions are best treated as quantifiers [Bostock] |
13817 | Definite descriptions are usually treated like names, and are just like them if they uniquely refer [Bostock] |
13848 | We are only obliged to treat definite descriptions as non-names if only the former have scope [Bostock] |
13813 | Definite descriptions don't always pick out one thing, as in denials of existence, or errors [Bostock] |
13815 | Names do not have scope problems (e.g. in placing negation), but Russell's account does have that problem [Bostock] |
13438 | 'Prenex normal form' is all quantifiers at the beginning, out of the scope of truth-functors [Bostock] |
13818 | If we allow empty domains, we must allow empty names [Bostock] |
18123 | Substitutional quantification is just standard if all objects in the domain have a name [Bostock] |
13801 | An 'informal proof' is in no particular system, and uses obvious steps and some ordinary English [Bostock] |
13619 | Quantification adds two axiom-schemas and a new rule [Bostock] |
13622 | Axiom systems from Frege, Russell, Church, Lukasiewicz, Tarski, Nicod, Kleene, Quine... [Bostock] |
13615 | 'Conditonalised' inferences point to the Deduction Theorem: If Γ,φ|-ψ then Γ|-φ→ψ [Bostock] |
13620 | Proof by Assumptions can always be reduced to Proof by Axioms, using the Deduction Theorem [Bostock] |
13621 | The Deduction Theorem and Reductio can 'discharge' assumptions - they aren't needed for the new truth [Bostock] |
13616 | The Deduction Theorem greatly simplifies the search for proof [Bostock] |
18120 | The Deduction Theorem is what licenses a system of natural deduction [Bostock] |
13753 | Natural deduction takes proof from assumptions (with its rules) as basic, and axioms play no part [Bostock] |
13755 | Excluded middle is an introduction rule for negation, and ex falso quodlibet will eliminate it [Bostock] |
13758 | In natural deduction we work from the premisses and the conclusion, hoping to meet in the middle [Bostock] |
13754 | Natural deduction rules for → are the Deduction Theorem (→I) and Modus Ponens (→E) [Bostock] |
13611 | Tableau proofs use reduction - seeking an impossible consequence from an assumption [Bostock] |
13613 | A completed open branch gives an interpretation which verifies those formulae [Bostock] |
13612 | Non-branching rules add lines, and branching rules need a split; a branch with a contradiction is 'closed' [Bostock] |
13761 | In a tableau proof no sequence is established until the final branch is closed; hypotheses are explored [Bostock] |
13757 | Unlike natural deduction, semantic tableaux have recipes for proving things [Bostock] |
13756 | A tree proof becomes too broad if its only rule is Modus Ponens [Bostock] |
13762 | Tableau rules are all elimination rules, gradually shortening formulae [Bostock] |
13759 | Each line of a sequent calculus is a conclusion of previous lines, each one explicitly recorded [Bostock] |
13760 | A sequent calculus is good for comparing proof systems [Bostock] |
13364 | Interpretation by assigning objects to names, or assigning them to variables first [Bostock, by PG] |
13821 | Extensionality is built into ordinary logic semantics; names have objects, predicates have sets of objects [Bostock] |
13362 | If an object has two names, truth is undisturbed if the names are swapped; this is Extensionality [Bostock] |
13541 | For 'negation-consistent', there is never |-(S)φ and |-(S)¬φ [Bostock] |
13542 | A proof-system is 'absolutely consistent' iff we don't have |-(S)φ for every formula [Bostock] |
13540 | A set of formulae is 'inconsistent' when there is no interpretation which can make them all true [Bostock] |
13544 | Inconsistency or entailment just from functors and quantifiers is finitely based, if compact [Bostock] |
13618 | Compactness means an infinity of sequents on the left will add nothing new [Bostock] |
18125 | Berry's Paradox considers the meaning of 'The least number not named by this name' [Bostock] |
18101 | Each addition changes the ordinality but not the cardinality, prior to aleph-1 [Bostock] |
18100 | ω + 1 is a new ordinal, but its cardinality is unchanged [Bostock] |
18102 | A cardinal is the earliest ordinal that has that number of predecessors [Bostock] |
18106 | Aleph-1 is the first ordinal that exceeds aleph-0 [Bostock] |
18095 | Instead of by cuts or series convergence, real numbers could be defined by axioms [Bostock] |
18099 | The number of reals is the number of subsets of the natural numbers [Bostock] |
18093 | For Eudoxus cuts in rationals are unique, but not every cut makes a real number [Bostock] |
18110 | Infinitesimals are not actually contradictory, because they can be non-standard real numbers [Bostock] |
18156 | Modern axioms of geometry do not need the real numbers [Bostock] |
18097 | The Peano Axioms describe a unique structure [Bostock] |
13358 | Ordinary or mathematical induction assumes for the first, then always for the next, and hence for all [Bostock] |
13359 | Complete induction assumes for all numbers less than n, then also for n, and hence for all numbers [Bostock] |
18148 | Hume's Principle is a definition with existential claims, and won't explain numbers [Bostock] |
18145 | Many things will satisfy Hume's Principle, so there are many interpretations of it [Bostock] |
18149 | There are many criteria for the identity of numbers [Bostock] |
18143 | Frege makes numbers sets to solve the Caesar problem, but maybe Caesar is a set! [Bostock] |
18116 | Numbers can't be positions, if nothing decides what position a given number has [Bostock] |
18117 | Structuralism falsely assumes relations to other numbers are numbers' only properties [Bostock] |
18141 | Nominalism about mathematics is either reductionist, or fictionalist [Bostock] |
18157 | Nominalism as based on application of numbers is no good, because there are too many applications [Bostock] |
18150 | Actual measurement could never require the precision of the real numbers [Bostock] |
18158 | Ordinals are mainly used adjectively, as in 'the first', 'the second'... [Bostock] |
18127 | Simple type theory has 'levels', but ramified type theory has 'orders' [Bostock] |
18144 | Neo-logicists agree that HP introduces number, but also claim that it suffices for the job [Bostock] |
18147 | Neo-logicists meet the Caesar problem by saying Hume's Principle is unique to number [Bostock] |
18146 | If Hume's Principle is the whole story, that implies structuralism [Bostock] |
18129 | Many crucial logicist definitions are in fact impredicative [Bostock] |
18111 | Treating numbers as objects doesn't seem like logic, since arithmetic fixes their totality [Bostock] |
18159 | Higher cardinalities in sets are just fairy stories [Bostock] |
18155 | A fairy tale may give predictions, but only a true theory can give explanations [Bostock] |
18140 | The best version of conceptualism is predicativism [Bostock] |
18138 | Conceptualism fails to grasp mathematical properties, infinity, and objective truth values [Bostock] |
18131 | If abstracta only exist if they are expressible, there can only be denumerably many of them [Bostock] |
18134 | Predicativism makes theories of huge cardinals impossible [Bostock] |
18135 | If mathematics rests on science, predicativism may be the best approach [Bostock] |
18136 | If we can only think of what we can describe, predicativism may be implied [Bostock] |
18132 | The predicativity restriction makes a difference with the real numbers [Bostock] |
18133 | The usual definitions of identity and of natural numbers are impredicative [Bostock] |
18564 | Do categories store causal knowledge, or typical properties, or knowledge of individuals? [Machery] |
18604 | Are quick and slow categorisation the same process, or quite different? [Machery] |
18573 | For each category of objects (such as 'dog') an individual seems to have several concepts [Machery] |
18602 | A thing is classified if its features are likely to be generated by that category's causal laws [Machery] |
18565 | There may be ad hoc categories, such as the things to pack in your suitcase for a trip [Machery] |
13802 | Relations can be one-many (at most one on the left) or many-one (at most one on the right) [Bostock] |
14974 | A relation is 'Euclidean' if aRb and aRc imply bRc [Cresswell] |
13543 | A relation is not reflexive, just because it is transitive and symmetrical [Bostock] |
18570 | There may be several ways to individuate things like concepts [Machery] |
13847 | If non-existent things are self-identical, they are just one thing - so call it the 'null object' [Bostock] |
14975 | A de dicto necessity is true in all worlds, but not necessarily of the same thing in each world [Cresswell] |
13820 | The idea that anything which can be proved is necessary has a problem with empty names [Bostock] |
18616 | If a term doesn't pick out a kind, keeping it may block improvements in classification [Machery] |
18614 | Vertical arguments say eliminate a term if it picks out different natural kinds in different theories [Machery] |
18615 | Horizontal arguments say eliminate a term if it fails to pick out a natural kind [Machery] |
18609 | Psychologists use 'induction' as generalising a property from one category to another [Machery] |
18610 | 'Ampliative' induction infers that all members of a category have a feature found in some of them [Machery] |
18562 | Connectionists cannot distinguish concept-memories from their background, or the processes [Machery] |
18561 | We can identify a set of cognitive capacities which are 'higher order' [Machery] |
18574 | Concepts for categorisation and for induction may be quite different [Machery] |
18588 | Concept theories aim at their knowledge, processes, format, acquisition, and location [Machery] |
18611 | We should abandon 'concept', and just use 'prototype', 'exemplar' and 'theory' [Machery] |
18567 | In the philosophy of psychology, concepts are usually introduced as constituents of thoughts [Machery] |
18569 | In philosophy theories of concepts explain how our propositional attitudes have content [Machery] |
18563 | By 'concept' psychologists mean various sorts of representation or structure [Machery] |
18558 | Concept theorists examine their knowledge, format, processes, acquisition and location [Machery] |
18557 | Psychologists treat concepts as long-term knowledge bodies which lead to judgements [Machery] |
18560 | Psychologist treat concepts as categories [Machery] |
18592 | The concepts OBJECT or AGENT may be innate [Machery] |
18566 | Concepts should contain working memory, not long-term, because they control behaviour [Machery] |
18584 | One hybrid theory combines a core definition with a prototype for identification [Machery] |
18585 | Heterogeneous concepts might have conflicting judgements, where hybrid theories will not [Machery] |
18578 | Concepts as definitions was rejected, and concepts as prototypes, exemplars or theories proposed [Machery] |
18575 | The concepts for a class typically include prototypes, and exemplars, and theories [Machery] |
18591 | Classical theory can't explain facts like typical examples being categorised quicker [Machery] |
18583 | Many categories don't seem to have a definition [Machery] |
18590 | Classical theory implies variety in processing times, but this does not generally occur [Machery] |
18594 | Knowing typical properties of things is especially useful in induction [Machery] |
18593 | The term 'prototype' is used for both typical category members, and the representation [Machery] |
18595 | Prototype theories are based on computation of similarities with the prototype [Machery] |
18596 | Prototype theorists don't tell us how we select the appropriate prototype [Machery] |
18603 | Maybe concepts are not the typical properties, but the ideal properties [Machery] |
18605 | It is more efficient to remember the prototype, than repeatedly create it from exemplars [Machery] |
18606 | The prototype view predicts that typical members are easier to categorise [Machery] |
18597 | Concepts as exemplars are based on the knowledge of properties of each particular [Machery] |
18598 | Exemplar theories need to explain how the relevant properties are selected from a multitude of them [Machery] |
18599 | In practice, known examples take priority over the rest of the set of exemplars [Machery] |
18600 | Theory Theory says category concepts are knowledge stores explaining membership [Machery] |
18601 | Theory Theory says concepts are explanatory knowledge, and concepts form domains [Machery] |
18607 | Theory theorists rely on best explanation, rather than on similarities [Machery] |
18608 | If categorisation is not by similarity, it seems to rely on what properties things might have [Machery] |
18587 | The theory account is sometimes labelled as 'knowledge' or 'explanation' in approach [Machery] |
18577 | The word 'grandmother' may be two concepts, with a prototype and a definition [Machery] |
18589 | For behaviourists concepts are dispositions to link category members to names [Machery] |
18612 | Americans are more inclined to refer causally than the Chinese are [Machery] |
13363 | A (modern) predicate is the result of leaving a gap for the name in a sentence [Bostock] |
18121 | In logic a proposition means the same when it is and when it is not asserted [Bostock] |
18613 | Artifacts can be natural kinds, when they are the object of historical enquiry [Machery] |