87 ideas
| 5728 | The concept of truth was originated by the senses [Lucretius] |
| 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] |
| 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] |
| 14289 | There are some assertable conditionals one would reject if one learned the antecedent [Jackson, by Edgington] |
| 5702 | The senses are much the best way to distinguish true from false [Lucretius] |
| 5729 | If the senses are deceptive, reason, which rests on them, is even worse [Lucretius] |
| 5697 | The only possible standard for settling doubts is the foundation of the senses [Lucretius] |
| 5727 | Most supposed delusions of the senses are really misinterpretations by the mind [Lucretius] |
| 5714 | Even simple facts are hard to believe at first hearing [Lucretius] |
| 5718 | The mind is in the middle of the breast, because there we experience fear and joy [Lucretius] |
| 5717 | The mind is a part of a man, just like a hand or an eye [Lucretius] |
| 21387 | The separate elements and capacities of a mind cannot be distinguished [Lucretius] |
| 5709 | The actions of the mind are not determinate and passive, because atoms can swerve [Lucretius] |
| 5695 | Only bodies can touch one another [Lucretius] |
| 5711 | The earth is and always has been an insentient being [Lucretius] |
| 5712 | Particles may have sensation, but eggs turning into chicks suggests otherwise [Lucretius] |
| 5719 | The mind moves limbs, wakes the body up, changes facial expressions, which involve touch [Lucretius] |
| 5724 | Lions, foxes and deer have distinct characters because their minds share in their bodies [Lucretius] |
| 5713 | You needn't be made of laughing particles to laugh, so why not sensation from senseless seeds? [Lucretius] |
| 6611 | One man's meat is another man's poison [Lucretius] |
| 5730 | Our bodies weren't created to be used; on the contrary, their creation makes a use possible [Lucretius] |
| 5726 | The dead are no different from those who were never born [Lucretius] |
| 5705 | Nature only wants two things: freedom from pain, and pleasure [Lucretius] |
| 5716 | Nature runs the universe by herself without the aid of gods [Lucretius] |
| 5704 | There can be no centre in infinity [Lucretius] |
| 5703 | The universe must be limitless, since there could be nothing outside to limit it [Lucretius] |
| 5693 | Everything is created and fed by nature from atoms, and they return to atoms in death [Lucretius] |
| 5701 | If an object is infinitely subdivisible, it will be the same as the whole universe [Lucretius] |
| 5708 | In downward motion, atoms occasionally swerve slightly for no reason [Lucretius] |
| 17004 | Nothing can break the binding laws of eternity [Lucretius] |
| 5696 | If there were no space there could be no movement, or even creation [Lucretius] |
| 5706 | Atoms move themselves [Lucretius] |
| 5700 | It is quicker to break things up than to assemble them [Lucretius] |
| 5698 | We can only sense time by means of movement, or its absence [Lucretius] |
| 5715 | This earth is very unlikely to be the only one created [Lucretius] |
| 5694 | Nothing can be created by divine power out of nothing [Lucretius] |
| 5699 | If matter wasn't everlasting, everything would have disappeared by now [Lucretius] |
| 5707 | The universe can't have been created by gods, because it is too imperfect [Lucretius] |
| 5710 | Gods are tranquil and aloof, and have no need of or interest in us [Lucretius] |
| 5731 | Why does Jupiter never hurl lightning from a blue sky? [Lucretius] |
| 5720 | Spirit is mortal [Lucretius] |
| 5722 | For a separated spirit to remain sentient it would need sense organs attached to it [Lucretius] |
| 5725 | An immortal mind couldn't work harmoniously with a mortal body [Lucretius] |
| 5721 | The mind is very small smooth particles, which evaporate at death [Lucretius] |
| 5723 | If spirit is immortal and enters us at birth, why don't we remember a previous existence? [Lucretius] |