31 ideas
1542 | Diogenes of Apollonia was the last natural scientist [Diogenes of Apollonia, by Simplicius] |
17749 | Post proved the consistency of propositional logic in 1921 [Walicki] |
17765 | Propositional language can only relate statements as the same or as different [Walicki] |
17764 | Boolean connectives are interpreted as functions on the set {1,0} [Walicki] |
17752 | The empty set is useful for defining sets by properties, when the members are not yet known [Walicki] |
17753 | The empty set avoids having to take special precautions in case members vanish [Walicki] |
17759 | Ordinals play the central role in set theory, providing the model of well-ordering [Walicki] |
17741 | To determine the patterns in logic, one must identify its 'building blocks' [Walicki] |
17747 | A 'model' of a theory specifies interpreting a language in a domain to make all theorems true [Walicki] |
17748 | The L-S Theorem says no theory (even of reals) says more than a natural number theory [Walicki] |
17761 | A compact axiomatisation makes it possible to understand a field as a whole [Walicki] |
17763 | Axiomatic systems are purely syntactic, and do not presuppose any interpretation [Walicki] |
17757 | Members of ordinals are ordinals, and also subsets of ordinals [Walicki] |
17755 | Ordinals are the empty set, union with the singleton, and any arbitrary union of ordinals [Walicki] |
17756 | The union of finite ordinals is the first 'limit ordinal'; 2ω is the second... [Walicki] |
17760 | Two infinite ordinals can represent a single infinite cardinal [Walicki] |
17758 | Ordinals are transitive sets of transitive sets; or transitive sets totally ordered by inclusion [Walicki] |
18085 | Values that approach zero, becoming less than any quantity, are 'infinitesimals' [Cauchy] |
18084 | When successive variable values approach a fixed value, that is its 'limit' [Cauchy] |
17762 | In non-Euclidean geometry, all Euclidean theorems are valid that avoid the fifth postulate [Walicki] |
17754 | Inductive proof depends on the choice of the ordering [Walicki] |
489 | Each thing must be in some way unique [Diogenes of Apollonia] |
17742 | Scotus based modality on semantic consistency, instead of on what the future could allow [Walicki] |
483 | Start a thesis with something undisputable [Diogenes of Apollonia] |
1544 | Perception must be an internal matter, because we can fail to perceive when we are preoccupied [Diogenes of Apollonia, by Theophrastus] |
24042 | The older Diogenes said the soul is air, made of the smallest particles [Diogenes of Apollonia] |
5995 | Diogenes of Apollonia offered the first teleological account of cosmology [Diogenes of Apollonia, by Robinson,TM] |
488 | Air is divine, because it is in and around everything, and arranges everything [Diogenes of Apollonia] |
484 | Everything is ultimately a variation of one underlying thing [Diogenes of Apollonia] |
486 | Plants and animals can only come into existence if something fixes their species [Diogenes of Apollonia] |
485 | Things must retain their essential nature during change, or mixing would be impossible [Diogenes of Apollonia] |