68 ideas
| 7113 | Phenomenology assumes that all consciousness is of something [Sartre] |
| 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] |
| 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] |
| 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] |
| 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] |
| 10077 | A 'surjective' ('onto') function creates every element of the output set [Smith,P] |
| 10078 | An 'injective' ('one-to-one') function creates a distinct output element from each original [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] |
| 17809 | Gödel showed that the syntactic approach to the infinite is of limited value [Kreisel] |
| 17810 | The study of mathematical foundations needs new non-mathematical concepts [Kreisel] |
| 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] |
| 10851 | Robinson Arithmetic 'Q' has basic axioms, quantifiers and first-order logic [Smith,P] |
| 10852 | Robinson Arithmetic (Q) is not negation complete [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] |
| 7112 | The Cogito depends on a second-order experience, of being conscious of consciousness [Sartre] |
| 7114 | The consciousness that says 'I think' is not the consciousness that thinks [Sartre] |
| 7119 | Is the Cogito reporting an immediate experience of doubting, or the whole enterprise of doubting? [Sartre] |
| 7122 | We can never, even in principle, grasp other minds, because the Ego is self-conceiving [Sartre] |
| 7125 | A consciousness can conceive of no other consciousness than itself [Sartre] |
| 7108 | The eternal truth of 2+2=4 is what gives unity to the mind which regularly thinks it [Sartre] |
| 7111 | Consciousness exists as consciousness of itself [Sartre] |
| 22226 | Since we are a consciousness, Sartre entirely rejected the unconscious mind [Sartre, by Daigle] |
| 7107 | Intentionality defines, transcends and unites consciousness [Sartre] |
| 7109 | If you think of '2+2=4' as the content of thought, the self must be united transcendentally [Sartre] |
| 7106 | The Ego is not formally or materially part of consciousness, but is outside in the world [Sartre] |
| 7117 | How could two I's, the reflective and the reflected, communicate with each other? [Sartre] |
| 7123 | Knowing yourself requires an exterior viewpoint, which is necessarily false [Sartre] |
| 22225 | My ego is more intimate to me, but not more certain than other egos [Sartre] |
| 7124 | The Ego never appears except when we are not looking for it [Sartre] |
| 7116 | When we are unreflective (as when chasing a tram) there is no 'I' [Sartre] |
| 7120 | It is theoretically possible that the Ego consists entirely of false memories [Sartre] |
| 7110 | If the 'I' is transcendental, it unnecessarily splits consciousness in two [Sartre] |
| 7115 | Maybe it is the act of reflection that brings 'me' into existence [Sartre] |
| 7121 | The Ego only appears to reflection, so it is cut off from the World [Sartre] |
| 17811 | The natural conception of points ducks the problem of naming or constructing each point [Kreisel] |