77 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] |
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] |
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] |
10076 | The 'range' of a function is the set of elements in the output set created by the function [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] |
10079 | A 'bijective' function has one-to-one correspondence in both directions [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] |
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] |
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] |
10080 | 'Effective' means simple, unintuitive, independent, controlled, dumb, and terminating [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] |
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] |
10604 | Incompleteness results in arithmetic from combining addition and successor with multiplication [Smith,P] |
10848 | Multiplication only generates incompleteness if combined with addition and successor [Smith,P] |
10617 | The 'ancestral' of a relation is a new relation which creates a long chain of the original relation [Smith,P] |
20239 | Unlike us, the early Greeks thought envy was a good thing, and hope a bad thing [Hesiod, by Nietzsche] |
20489 | Human beings can never really flourish in a long-term state of nature [Wolff,J] |
20483 | Collective rationality is individuals doing their best, assuming others all do the same [Wolff,J] |
20532 | Should love be the first virtue of a society, as it is of the family? [Wolff,J] |
20490 | For utilitarians, consent to the state is irrelevant, if it produces more happiness [Wolff,J] |
20493 | Social contract theory has the attracton of including everyone, and being voluntary [Wolff,J] |
20494 | Maybe voting in elections is a grant of legitimacy to the winners [Wolff,J] |
20500 | We can see the 'general will' as what is in the general interest [Wolff,J] |
20497 | How can dictators advance the interests of the people, if they don't consult them about interests? [Wolff,J] |
20506 | 'Separation of powers' allows legislative, executive and judicial functions to monitor one another [Wolff,J] |
20530 | Political choice can be by utility, or maximin, or maximax [Wolff,J] |
20487 | A realistic and less utopian anarchism looks increasingly like liberal democracy [Wolff,J] |
20488 | It is hard for anarchists to deny that we need experts [Wolff,J] |
20529 | Utilitarianism probably implies a free market plus welfare [Wolff,J] |
20510 | A system of democracy which includes both freedom and equality is almost impossible [Wolff,J] |
20511 | Democracy expresses equal respect (which explains why criminals forfeit the vote) [Wolff,J] |
20502 | Democracy has been seen as consistent with many types of inequality [Wolff,J] |
20496 | A true democracy could not tolerate slavery, exploitation or colonialism [Wolff,J] |
20498 | We should decide whether voting is for self-interests, or for the common good [Wolff,J] |
20499 | Condorcet proved that sensible voting leads to an emphatically right answer [Wolff,J] |
20509 | Occasional defeat is acceptable, but a minority that is continually defeated is a problem [Wolff,J] |
20524 | Market prices indicate shortages and gluts, and where the profits are to be made [Wolff,J] |
20518 | Liberty principles can't justify laws against duelling, incest between siblings and euthanasia [Wolff,J] |
20531 | Either Difference allows unequal liberty, or Liberty makes implementing Difference impossible [Wolff,J] |
20526 | Utilitarians argue for equal distribution because of diminishing utility of repetition [Wolff,J] |
20528 | Difference Principle: all inequalities should be in favour of the disadvantaged [Wolff,J] |
20503 | Political equality is not much use without social equality [Wolff,J] |
20513 | If natural rights are axiomatic, there is then no way we can defend them [Wolff,J] |
20512 | Standard rights: life, free speech, assembly, movement, vote, stand (plus shelter, food, health?) [Wolff,J] |
20514 | If rights are natural, rather than inferred, how do we know which rights we have? [Wolff,J] |
20522 | Utilitarians might say property ownership encourages the best use of the land [Wolff,J] |
20534 | Rights and justice are only the last resorts of a society, something to fall back on [Wolff,J] |
20492 | Following some laws is not a moral matter; trivial traffic rules, for example [Wolff,J] |