30 ideas
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] |
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] |
16740 | A power is not a cause, but an aptitude for a cause [Zabarella] |
17742 | Scotus based modality on semantic consistency, instead of on what the future could allow [Walicki] |
7127 | If men are good you should keep promises, but they aren't, so you needn't [Machiavelli] |
6309 | The principle foundations of all states are good laws and good armies [Machiavelli] |
6305 | To retain a conquered state, wipe out the ruling family, and preserve everything else [Machiavelli] |
6306 | People are vengeful, so be generous to them, or destroy them [Machiavelli] |
6308 | A sensible conqueror does all his harmful deeds immediately, because people soon forget [Machiavelli] |
6307 | A desire to conquer, and men who do it, are always praised, or not blamed [Machiavelli] |
19813 | All legislators invoke God in support of extraordinary laws, because their justification is not obvious [Machiavelli] |
7126 | Rulers should preserve the foundations of religion, to ensure good behaviour and unity [Machiavelli] |
7486 | Machiavelli emancipated politics from religion [Machiavelli, by Watson] |
16571 | Prime matter is exceptionally obscure [Zabarella] |