95 ideas
| 13466 | We are all post-Kantians, because he set the current agenda for philosophy [Hart,WD] |
| 13477 | The problems are the monuments of philosophy [Hart,WD] |
| 23183 | Different abilities are needed for living in an incomplete and undogmatic system [Nietzsche] |
| 23188 | Bad writers use shapeless floating splotches of concepts [Nietzsche] |
| 13515 | To study abstract problems, some knowledge of set theory is essential [Hart,WD] |
| 23212 | A text has many interpretations, but no 'correct' one [Nietzsche] |
| 23199 | What is the search for truth if it isn't moral? [Nietzsche] |
| 23202 | Like all philosophers, I love truth [Nietzsche] |
| 13469 | Tarski showed how we could have a correspondence theory of truth, without using 'facts' [Hart,WD] |
| 13504 | Truth for sentences is satisfaction of formulae; for sentences, either all sequences satisfy it (true) or none do [Hart,WD] |
| 13503 | A first-order language has an infinity of T-sentences, which cannot add up to a definition of truth [Hart,WD] |
| 13500 | Conditional Proof: infer a conditional, if the consequent can be deduced from the antecedent [Hart,WD] |
| 13502 | ∃y... is read as 'There exists an individual, call it y, such that...', and not 'There exists a y such that...' [Hart,WD] |
| 13456 | Set theory articulates the concept of order (through relations) [Hart,WD] |
| 13497 | Nowadays ZFC and NBG are the set theories; types are dead, and NF is only useful for the whole universe [Hart,WD] |
| 10888 | Sets can be defined by 'enumeration', or by 'abstraction' (based on a property) [Zalabardo] |
| 13443 | ∈ relates across layers, while ⊆ relates within layers [Hart,WD] |
| 10889 | The 'Cartesian Product' of two sets relates them by pairing every element with every element [Zalabardo] |
| 10890 | A 'partial ordering' is reflexive, antisymmetric and transitive [Zalabardo] |
| 13442 | Without the empty set we could not form a∩b without checking that a and b meet [Hart,WD] |
| 10886 | Determinacy: an object is either in a set, or it isn't [Zalabardo] |
| 13493 | In the modern view, foundation is the heart of the way to do set theory [Hart,WD] |
| 13495 | Foundation Axiom: an nonempty set has a member disjoint from it [Hart,WD] |
| 13461 | We can choose from finite and evident sets, but not from infinite opaque ones [Hart,WD] |
| 13462 | With the Axiom of Choice every set can be well-ordered [Hart,WD] |
| 10887 | Specification: Determinate totals of objects always make a set [Zalabardo] |
| 13516 | If we accept that V=L, it seems to settle all the open questions of set theory [Hart,WD] |
| 13441 | Naïve set theory has trouble with comprehension, the claim that every predicate has an extension [Hart,WD] |
| 13494 | The iterative conception may not be necessary, and may have fixed points or infinitely descending chains [Hart,WD] |
| 13457 | A 'partial ordering' is irreflexive and transitive; the sets are ordered, but not the subsets [Hart,WD] |
| 13458 | A partial ordering becomes 'total' if any two members of its field are comparable [Hart,WD] |
| 13460 | 'Well-ordering' must have a least member, so it does the natural numbers but not the integers [Hart,WD] |
| 13490 | Von Neumann defines α<β as α∈β [Hart,WD] |
| 13481 | Maybe sets should be rethought in terms of the even more basic categories [Hart,WD] |
| 10897 | A first-order 'sentence' is a formula with no free variables [Zalabardo] |
| 10893 | Γ |= φ for sentences if φ is true when all of Γ is true [Zalabardo] |
| 10899 | Γ |= φ if φ is true when all of Γ is true, for all structures and interpretations [Zalabardo] |
| 23196 | Logic is a fiction, which invents the view that one thought causes another [Nietzsche] |
| 10896 | Propositional logic just needs ¬, and one of ∧, ∨ and → [Zalabardo] |
| 13506 | The universal quantifier can't really mean 'all', because there is no universal set [Hart,WD] |
| 10898 | The semantics shows how truth values depend on instantiations of properties and relations [Zalabardo] |
| 10902 | We can do semantics by looking at given propositions, or by building new ones [Zalabardo] |
| 10892 | We make a truth assignment to T and F, which may be true and false, but merely differ from one another [Zalabardo] |
| 10895 | 'Logically true' (|= φ) is true for every truth-assignment [Zalabardo] |
| 10900 | Logically true sentences are true in all structures [Zalabardo] |
| 10894 | A sentence-set is 'satisfiable' if at least one truth-assignment makes them all true [Zalabardo] |
| 10901 | Some formulas are 'satisfiable' if there is a structure and interpretation that makes them true [Zalabardo] |
| 10903 | A structure models a sentence if it is true in the model, and a set of sentences if they are all true in the model [Zalabardo] |
| 13513 | Models are ways the world might be from a first-order point of view [Hart,WD] |
| 13512 | Modern model theory begins with the proof of Los's Conjecture in 1962 [Hart,WD] |
| 13505 | Model theory studies how set theory can model sets of sentences [Hart,WD] |
| 13511 | Model theory is mostly confined to first-order theories [Hart,WD] |
| 13496 | First-order logic is 'compact': consequences of a set are consequences of a finite subset [Hart,WD] |
| 13484 | Berry's Paradox: we succeed in referring to a number, with a term which says we can't do that [Hart,WD] |
| 13482 | The Burali-Forti paradox is a crisis for Cantor's ordinals [Hart,WD] |
| 13507 | The machinery used to solve the Liar can be rejigged to produce a new Liar [Hart,WD] |
| 23186 | Numbers enable us to manage the world - to the limits of counting [Nietzsche] |
| 13459 | The less-than relation < well-orders, and partially orders, and totally orders the ordinal numbers [Hart,WD] |
| 13491 | The axiom of infinity with separation gives a least limit ordinal ω [Hart,WD] |
| 13463 | There are at least as many infinite cardinals as transfinite ordinals (because they will map) [Hart,WD] |
| 13492 | Von Neumann's ordinals generalise into the transfinite better, because Zermelo's ω is a singleton [Hart,WD] |
| 13446 | 19th century arithmetization of analysis isolated the real numbers from geometry [Hart,WD] |
| 13509 | We can establish truths about infinite numbers by means of induction [Hart,WD] |
| 13474 | Euclid has a unique parallel, spherical geometry has none, and saddle geometry has several [Hart,WD] |
| 10891 | If a set is defined by induction, then proof by induction can be applied to it [Zalabardo] |
| 13471 | Mathematics makes existence claims, but philosophers usually say those are never analytic [Hart,WD] |
| 23211 | Events are just interpretations of groups of appearances [Nietzsche] |
| 13488 | Mass words do not have plurals, or numerical adjectives, or use 'fewer' [Hart,WD] |
| 23201 | The 'I' does not think; it is a construction of thinking, like other useful abstractions [Nietzsche] |
| 23207 | Appearance is the sole reality of things, to which all predicates refer [Nietzsche] |
| 13480 | Fregean self-evidence is an intrinsic property of basic truths, rules and definitions [Hart,WD] |
| 13476 | The failure of key assumptions in geometry, mereology and set theory throw doubt on the a priori [Hart,WD] |
| 23197 | Memory is essential, and is only possible by means of abbreviation signs [Nietzsche] |
| 23206 | Schematic minds think thoughts are truer if they slot into a scheme [Nietzsche] |
| 23209 | Each of our personal drives has its own perspective [Nietzsche] |
| 23184 | The mind is a simplifying apparatus [Nietzsche] |
| 23190 | Consciousness is our awareness of our own mental life [Nietzsche] |
| 23191 | Minds have an excluding drive to scare things off, and a selecting one to filter facts [Nietzsche] |
| 23213 | The greatest drive of life is to discharge strength, rather than preservation [Nietzsche] |
| 23210 | That all events are necessary does not mean they are compelled [Nietzsche] |
| 23189 | Concepts are rough groups of simultaneous sensations [Nietzsche] |
| 23192 | Concepts don’t match one thing, but many things a little bit [Nietzsche] |
| 23187 | Whatever their origin, concepts survive by being useful [Nietzsche] |
| 13475 | The Fregean concept of GREEN is a function assigning true to green things, and false to the rest [Hart,WD] |
| 23205 | Thought starts as ambiguity, in need of interpretation and narrowing [Nietzsche] |
| 23198 | Aesthetics can be more basic than morality, in our pleasure in certain patterns of experience [Nietzsche] |
| 23208 | Caesar and Napoleon point to the future, when they pursue their task regardless of human sacrifice [Nietzsche] |
| 23193 | Napoleon was very focused, and rightly ignored compassion [Nietzsche] |
| 23214 | For the strongest people, nihilism gives you wings! [Nietzsche] |
| 23203 | The great question is approaching, of how to govern the earth as a whole [Nietzsche] |
| 23200 | The controlling morality of aristocracy is the desire to resemble their ancestors [Nietzsche] |
| 23194 | People feel united as a nation by one language, but then want a common ancestry and history [Nietzsche] |
| 23204 | To be someone you need property, and wanting more is healthy [Nietzsche] |
| 23195 | Laws of nature are actually formulas of power relations [Nietzsche] |
| 23185 | In chemistry every substance pushes, and thus creates new substances [Nietzsche] |