59 ideas
14027 | If we are to use words in enquiry, we need their main, unambiguous and uncontested meanings [Epicurus] |
14040 | Observation and applied thought are always true [Epicurus] |
13520 | A 'tautology' must include connectives [Wolf,RS] |
13524 | Deduction Theorem: T∪{P}|-Q, then T|-(P→Q), which justifies Conditional Proof [Wolf,RS] |
13522 | Universal Generalization: If we prove P(x) with no special assumptions, we can conclude ∀xP(x) [Wolf,RS] |
13521 | Universal Specification: ∀xP(x) implies P(t). True for all? Then true for an instance [Wolf,RS] |
13523 | Existential Generalization (or 'proof by example'): if we can say P(t), then we can say something is P [Wolf,RS] |
13529 | Empty Set: ∃x∀y ¬(y∈x). The unique empty set exists [Wolf,RS] |
13526 | Comprehension Axiom: if a collection is clearly specified, it is a set [Wolf,RS] |
13534 | In first-order logic syntactic and semantic consequence (|- and |=) nicely coincide [Wolf,RS] |
13535 | First-order logic is weakly complete (valid sentences are provable); we can't prove every sentence or its negation [Wolf,RS] |
13531 | Model theory reveals the structures of mathematics [Wolf,RS] |
13532 | Model theory 'structures' have a 'universe', some 'relations', some 'functions', and some 'constants' [Wolf,RS] |
13519 | Model theory uses sets to show that mathematical deduction fits mathematical truth [Wolf,RS] |
13533 | First-order model theory rests on completeness, compactness, and the Löwenheim-Skolem-Tarski theorem [Wolf,RS] |
13537 | An 'isomorphism' is a bijection that preserves all structural components [Wolf,RS] |
13539 | The LST Theorem is a serious limitation of first-order logic [Wolf,RS] |
13538 | If a theory is complete, only a more powerful language can strengthen it [Wolf,RS] |
13525 | Most deductive logic (unlike ordinary reasoning) is 'monotonic' - we don't retract after new givens [Wolf,RS] |
13530 | An ordinal is an equivalence class of well-orderings, or a transitive set whose members are transitive [Wolf,RS] |
17518 | Counting 'coin in this box' may have coin as the unit, with 'in this box' merely as the scope [Ayers] |
17516 | If counting needs a sortal, what of things which fall under two sortals? [Ayers] |
13518 | Modern mathematics has unified all of its objects within set theory [Wolf,RS] |
14028 | Nothing comes to be from what doesn't exist [Epicurus] |
14029 | If disappearing things went to nothingness, nothing could return, and it would all be gone by now [Epicurus] |
14030 | The totality is complete, so there is no room for it to change, and nothing extraneous to change it [Epicurus] |
17520 | Events do not have natural boundaries, and we have to set them [Ayers] |
14048 | Astronomical movements are blessed, but they don't need the help of the gods [Epicurus] |
14044 | The perceived accidental properties of bodies cannot be conceived of as independent natures [Epicurus] |
14045 | Accidental properties give a body its nature, but are not themselves bodies or parts of bodies [Epicurus] |
17519 | To express borderline cases of objects, you need the concept of an 'object' [Ayers] |
17510 | Speakers need the very general category of a thing, if they are to think about it [Ayers] |
17522 | We use sortals to classify physical objects by the nature and origin of their unity [Ayers] |
17515 | Seeing caterpillar and moth as the same needs continuity, not identity of sortal concepts [Ayers] |
17511 | Recognising continuity is separate from sortals, and must precede their use [Ayers] |
17517 | Could the same matter have more than one form or principle of unity? [Ayers] |
14046 | A 'body' is a conception of an aggregate, with properties defined by application conditions [Epicurus] |
17513 | If there are two objects, then 'that marble, man-shaped object' is ambiguous [Ayers] |
17523 | Sortals basically apply to individuals [Ayers] |
14047 | Bodies have impermanent properties, and permanent ones which define its conceived nature [Epicurus] |
17521 | You can't have the concept of a 'stage' if you lack the concept of an object [Ayers] |
17514 | Temporal 'parts' cannot be separated or rearranged [Ayers] |
17509 | Some say a 'covering concept' completes identity; others place the concept in the reference [Ayers] |
17512 | If diachronic identities need covering concepts, why not synchronic identities too? [Ayers] |
14039 | Above and below us will never appear to be the same, because it is inconceivable [Epicurus] |
14050 | We aim to dissolve our fears, by understanding their causes [Epicurus] |
14037 | Atoms only have shape, weight and size, and the properties which accompany shape [Epicurus] |
6010 | Illusions are not false perceptions, as we accurately perceive the pattern of atoms [Epicurus, by Modrak] |
14041 | The soul is fine parts distributed through the body, resembling hot breath [Epicurus] |
14042 | The soul cannot be incorporeal, because then it could neither act nor be acted upon [Epicurus] |
14032 | Totality has no edge; an edge implies a contrast beyond the edge, and there can't be one [Epicurus] |
14033 | Bodies are unlimited as well as void, since the two necessarily go together [Epicurus] |
14034 | There exists an infinity of each shape of atom, but the number of shapes is beyond our knowledge [Epicurus] |
14035 | Atoms just have shape, size and weight; colour results from their arrangement [Epicurus] |
14038 | There cannot be unlimited division, because it would reduce things to non-existence [Epicurus] |
14049 | We aim to know the natures which are observed in natural phenomena [Epicurus] |
14043 | The void cannot interact, but just gives the possibility of motion [Epicurus] |
14031 | Space must exist, since movement is obvious, and there must be somewhere to move in [Epicurus] |
14036 | There are endless cosmoi, some like and some unlike this one [Epicurus] |