66 ideas
10073 | There cannot be a set theory which is complete [Smith,P] |
10616 | Second-order arithmetic can prove new sentences of first-order [Smith,P] |
10076 | The 'range' of a function is the set of elements in the output set created by the function [Smith,P] |
10605 | Two functions are the same if they have the same extension [Smith,P] |
10075 | A 'partial function' maps only some elements to another set [Smith,P] |
10074 | A 'total function' maps every element to one element in another set [Smith,P] |
10612 | An argument is a 'fixed point' for a function if it is mapped back to itself [Smith,P] |
10615 | The Comprehension Schema says there is a property only had by things satisfying a condition [Smith,P] |
10595 | A 'theorem' of a theory is a sentence derived from the axioms using the proof system [Smith,P] |
10602 | A 'natural deduction system' has no axioms but many rules [Smith,P] |
10613 | No nice theory can define truth for its own language [Smith,P] |
10078 | An 'injective' ('one-to-one') function creates a distinct output element from each original [Smith,P] |
10077 | A 'surjective' ('onto') function creates every element of the output set [Smith,P] |
10079 | A 'bijective' function has one-to-one correspondence in both directions [Smith,P] |
10070 | If everything that a theory proves is true, then it is 'sound' [Smith,P] |
10086 | Soundness is true axioms and a truth-preserving proof system [Smith,P] |
10596 | A theory is 'sound' iff every theorem is true (usually from true axioms and truth-preservation) [Smith,P] |
10598 | A theory is 'negation complete' if it proves all sentences or their negation [Smith,P] |
10597 | 'Complete' applies both to whole logics, and to theories within them [Smith,P] |
10069 | A theory is 'negation complete' if one of its sentences or its negation can always be proved [Smith,P] |
10609 | Two routes to Incompleteness: semantics of sound/expressible, or syntax of consistency/proof [Smith,P] |
10080 | 'Effective' means simple, unintuitive, independent, controlled, dumb, and terminating [Smith,P] |
10087 | A theory is 'decidable' if all of its sentences could be mechanically proved [Smith,P] |
10088 | Any consistent, axiomatized, negation-complete formal theory is decidable [Smith,P] |
10081 | A set is 'enumerable' is all of its elements can result from a natural number function [Smith,P] |
10083 | A set is 'effectively enumerable' if a computer could eventually list every member [Smith,P] |
10084 | A finite set of finitely specifiable objects is always effectively enumerable (e.g. primes) [Smith,P] |
10085 | The set of ordered pairs of natural numbers <i,j> is effectively enumerable [Smith,P] |
10601 | The thorems of a nice arithmetic can be enumerated, but not the truths (so they're diffferent) [Smith,P] |
10600 | Being 'expressible' depends on language; being 'capture/represented' depends on axioms and proof system [Smith,P] |
10599 | For primes we write (x not= 1 ∧ ∀u∀v(u x v = x → (u = 1 ∨ v = 1))) [Smith,P] |
10610 | The reals contain the naturals, but the theory of reals doesn't contain the theory of naturals [Smith,P] |
10619 | The truths of arithmetic are just true equations and their universally quantified versions [Smith,P] |
10618 | All numbers are related to zero by the ancestral of the successor relation [Smith,P] |
10608 | The number of Fs is the 'successor' of the Gs if there is a single F that isn't G [Smith,P] |
10849 | Baby arithmetic covers addition and multiplication, but no general facts about numbers [Smith,P] |
10850 | Baby Arithmetic is complete, but not very expressive [Smith,P] |
10852 | Robinson Arithmetic (Q) is not negation complete [Smith,P] |
10851 | Robinson Arithmetic 'Q' has basic axioms, quantifiers and first-order logic [Smith,P] |
10068 | Natural numbers have zero, unique successors, unending, no circling back, and no strays [Smith,P] |
10603 | The logic of arithmetic must quantify over properties of numbers to handle induction [Smith,P] |
10848 | Multiplication only generates incompleteness if combined with addition and successor [Smith,P] |
10604 | Incompleteness results in arithmetic from combining addition and successor with multiplication [Smith,P] |
10617 | The 'ancestral' of a relation is a new relation which creates a long chain of the original relation [Smith,P] |
8780 | Attributes are functions, not objects; this distinguishes 'square of 2' from 'double of 2' [Geach] |
11910 | Being 'the same' is meaningless, unless we specify 'the same X' [Geach] |
19513 | A contextualist coherentist will say that how strongly a justification must cohere depends on context [DeRose] |
19514 | Classical invariantism combines fixed truth-conditions with variable assertability standards [DeRose] |
19515 | We can make contextualism more precise, by specifying the discrimination needed each time [DeRose] |
19510 | In some contexts there is little more to knowledge than true belief. [DeRose] |
19516 | Contextualists worry about scepticism, but they should focus on the use of 'know' in ordinary speech [DeRose] |
19511 | If contextualism is about knowledge attribution, rather than knowledge, then it is philosophy of language [DeRose] |
8775 | A big flea is a small animal, so 'big' and 'small' cannot be acquired by abstraction [Geach] |
8776 | We cannot learn relations by abstraction, because their converse must be learned too [Geach] |
2567 | You can't define real mental states in terms of behaviour that never happens [Geach] |
2568 | Beliefs aren't tied to particular behaviours [Geach] |
8781 | The mind does not lift concepts from experience; it creates them, and then applies them [Geach] |
8769 | If someone has aphasia but can still play chess, they clearly have concepts [Geach] |
8770 | 'Abstractionism' is acquiring a concept by picking out one experience amongst a group [Geach] |
8771 | 'Or' and 'not' are not to be found in the sensible world, or even in the world of inner experience [Geach] |
8772 | We can't acquire number-concepts by extracting the number from the things being counted [Geach] |
8773 | Abstractionists can't explain counting, because it must precede experience of objects [Geach] |
8774 | The numbers don't exist in nature, so they cannot have been abstracted from there into our languages [Geach] |
8778 | Blind people can use colour words like 'red' perfectly intelligently [Geach] |
8777 | If 'black' and 'cat' can be used in the absence of such objects, how can such usage be abstracted? [Geach] |
8779 | We can form two different abstract concepts that apply to a single unified experience [Geach] |