38 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] |
| 6410 | The only real proper names are 'this' and 'that'; the rest are really definite descriptions. [Russell, by Grayling] |
| 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] |
| 17763 | Axiomatic systems are purely syntactic, and do not presuppose any interpretation [Walicki] |
| 17761 | A compact axiomatisation makes it possible to understand a field as a whole [Walicki] |
| 17757 | Members of ordinals are ordinals, and also subsets of ordinals [Walicki] |
| 17758 | Ordinals are transitive sets of transitive sets; or transitive sets totally ordered by inclusion [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] |
| 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] |
| 17742 | Scotus based modality on semantic consistency, instead of on what the future could allow [Walicki] |
| 23154 | We divide mankind into friend and foe, and cooperate with one and compete with the other [Russell] |
| 23153 | Gradually loyalty to a creed increased, which could even outweigh nationality [Russell] |
| 23152 | Increasingly war expands communities, and unifies them through fear [Russell] |
| 23155 | In early societies the leaders needed cohesion, but the rest just had to obey [Russell] |
| 23156 | The economic and political advantages of great size seem to have no upper limit [Russell] |
| 23157 | Government has a negative purpose, to prevent trouble, and a positive aim of realising our desires [Russell] |
| 23151 | A monarch is known to everyone in the group, and can thus unite large groups [Russell] |
| 23167 | Power should be with smaller bodies, as long as it doesn't restrict central powers [Russell] |
| 23168 | A state is essential, to control greedy or predatory impulses [Russell] |
| 23163 | In an anarchy universities, research, books, and even seaside holidays, would be impossible [Russell] |
| 23166 | In democracy we are more aware of being governed than of our tiny share in government [Russell] |
| 23162 | Managers are just as remote from workers under nationalisation as under capitalism [Russell] |
| 23165 | Socialists say economic justice needs some state control of industries, and of foreign trade [Russell] |
| 23160 | Being a slave of society is hardly better than being a slave of a despot [Russell] |
| 23158 | Slavery began the divorce between the work and the purposes of the worker [Russell] |
| 23161 | Slaves can be just as equal as free people [Russell] |
| 23159 | Scarce goods may be denied entirely, to avoid their unequal distribution [Russell] |
| 23164 | Modern justice is seen as equality, apart from modest extra rewards for exceptional desert [Russell] |