34 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] |
| 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] |
| 17757 | Members of ordinals are ordinals, and also subsets of ordinals [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] |
| 6248 | Reason is too slow and doubtful to guide all actions, which need external and moral senses [Hutcheson] |
| 6238 | We approve of actions by a superior moral sense [Hutcheson] |
| 6239 | We dislike a traitor, even if they give us great benefit [Hutcheson] |
| 6240 | The moral sense is not an innate idea, but an ability to approve or disapprove in a disinterested way [Hutcheson] |
| 6242 | We cannot choose our moral feelings, otherwise bribery could affect them [Hutcheson] |
| 6247 | Everyone feels uneasy when seeing others in pain, unless the others are evil [Hutcheson] |
| 6244 | Human nature seems incapable of universal malice, except what results from self-love [Hutcheson] |
| 6243 | As death approaches, why do we still care about family, friends or country? [Hutcheson] |
| 6246 | My action is not made good by a good effect, if I did not foresee and intend it [Hutcheson] |
| 7903 | The six perfections are giving, morality, patience, vigour, meditation, and wisdom [Nagarjuna] |
| 6241 | Contempt of danger is just madness if it is not in some worthy cause [Hutcheson] |
| 6245 | That action is best, which procures the greatest happiness for the greatest number [Hutcheson] |
| 6251 | The loss of perfect rights causes misery, but the loss of imperfect rights reduces social good [Hutcheson] |
| 6250 | We say God is good if we think everything he does aims at the happiness of his creatures [Hutcheson] |
| 6249 | If goodness is constituted by God's will, it is a tautology to say God's will is good [Hutcheson] |