99 ideas
| 24047 | An account is either a definition or a demonstration [Aristotle] |
| 24052 | From one thing alone we can infer its contrary [Aristotle] |
| 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] |
| 1729 | We perceive number by the denial of continuity [Aristotle] |
| 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] |
| 24057 | What is prior is always potentially present in what is next in order [Aristotle] |
| 10617 | The 'ancestral' of a relation is a new relation which creates a long chain of the original relation [Smith,P] |
| 16752 | Sight is the essence of the eye, fitting its definition; the eye itself is just the matter [Aristotle] |
| 24058 | The substance is the cause of a thing's being [Aristotle] |
| 24055 | Matter is potential, form is actual [Aristotle] |
| 24040 | Scientists explain anger by the matter, dialecticians by the form and the account [Aristotle] |
| 5051 | The intellect has potential to think, like a tablet on which nothing has yet been written [Aristotle] |
| 16723 | Perception of sensible objects is virtually never wrong [Aristotle] |
| 1724 | Perception necessitates pleasure and pain, which necessitates appetite [Aristotle] |
| 1730 | Why do we have many senses, and not just one? [Aristotle] |
| 17711 | Our minds take on the form of what is being perceived [Aristotle, by Mares] |
| 1725 | Why can't we sense the senses? And why do senses need stimuli? [Aristotle] |
| 1732 | Sense organs aren't the end of sensation, or they would know what does the sensing [Aristotle] |
| 1728 | Many objects of sensation are common to all the senses [Aristotle] |
| 1727 | Some objects of sensation are unique to one sense, where deception is impossible [Aristotle] |
| 1734 | In moral thought images are essential, to be pursued or avoided [Aristotle] |
| 1726 | We may think when we wish, but not perceive, because universals are within the mind [Aristotle] |
| 16647 | Demonstration starts from a definition of essence, so we can derive (or conjecture about) the properties [Aristotle] |
| 24048 | Demonstrations move from starting-points to deduced conclusions [Aristotle] |
| 16646 | To understand a triangle summing to two right angles, we need to know the essence of a line [Aristotle] |
| 1714 | Mind involves movement, perception, incorporeality [Aristotle] |
| 5507 | Aristotle led to the view that there are several souls, all somewhat physical [Aristotle, by Martin/Barresi] |
| 24051 | Soul is seen as what moves, or what is least physical, or a combination of elements [Aristotle] |
| 12086 | Psuché is the form and actuality of a body which potentially has life [Aristotle] |
| 16754 | The soul is the cause or source of movement, the essence of body, and its end [Aristotle] |
| 24046 | Understanding is impossible, if it involves the understanding having parts [Aristotle] |
| 1717 | If the soul is composed of many physical parts, it can't be a true unity [Aristotle] |
| 24053 | If a soul have parts, what unites them? [Aristotle] |
| 1721 | What unifies the soul would have to be a super-soul, which seems absurd [Aristotle] |
| 1735 | In a way the soul is everything which exists, through its perceptions and thoughts [Aristotle] |
| 24061 | If we divide the mind up according to its capacities, there are a lot of them [Aristotle] |
| 24062 | Self-moving animals must have desires, and that entails having imagination [Aristotle] |
| 1710 | Emotion involves the body, thinking uses the mind, imagination hovers between them [Aristotle] |
| 24039 | All the emotions seem to involve the body, simultaneously with the feeling [Aristotle] |
| 24056 | The soul (or parts of it) is not separable from the body [Aristotle] |
| 24050 | If soul is separate from body, why does it die when the body dies? [Aristotle] |
| 24049 | Thinkers place the soul within the body, but never explain how they are attached [Aristotle] |
| 1514 | Early thinkers concentrate on the soul but ignore the body, as if it didn't matter what body received the soul [Aristotle] |
| 2683 | Aristotle has a problem fitting his separate reason into the soul, which is said to be the form of the body [Ackrill on Aristotle] |
| 1718 | Does the mind think or pity, or does the whole man do these things? [Aristotle] |
| 13275 | The soul and the body are inseparable, like the imprint in some wax [Aristotle] |
| 1733 | Thinking is not perceiving, but takes the form of imagination and speculation [Aristotle] |
| 23307 | Aristotle makes belief a part of reason, but sees desires as separate [Aristotle, by Sorabji] |
| 24060 | Self-controlled follow understanding, when it is opposed to desires [Aristotle] |
| 4376 | Pleasure and pain are perceptions of things as good or bad [Aristotle] |
| 1740 | Nature does nothing in vain [Aristotle] |
| 4398 | An event causes another just if the second event would not have happened without the first [Lewis, by Psillos] |
| 24045 | Movement is spatial, alteration, withering or growth [Aristotle] |
| 1738 | Practical reason is based on desire, so desire must be the ultimate producer of movement [Aristotle] |
| 24044 | Movement can be intrinsic (like a ship) or relative (like its sailors) [Aristotle] |
| 1739 | If all movement is either pushing or pulling, there must be a still point in between where it all starts [Aristotle] |
| 24064 | If something is pushed, it pushes back [Aristotle] |
| 24063 | What is born has growth, a prime, and a withering away [Aristotle] |