77 ideas
16123 | Whenever you perceive a community of things, you should also hunt out differences in the group [Plato] |
23770 | Reductive analysis makes a concept clearer, by giving an alternative simpler set [Williams,NE] |
16125 | To reveal a nature, divide down, and strip away what it has in common with other things [Plato] |
16124 | No one wants to define 'weaving' just for the sake of weaving [Plato] |
23769 | Promoting an ontology by its implied good metaphysic is an 'argument-by-display' [Williams,NE] |
13689 | 'Theorems' are formulas provable from no premises at all [Sider] |
13705 | Truth tables assume truth functionality, and are just pictures of truth functions [Sider] |
13706 | Intuitively, deontic accessibility seems not to be reflexive, but to be serial [Sider] |
13710 | In D we add that 'what is necessary is possible'; then tautologies are possible, and contradictions not necessary [Sider] |
13711 | System B introduces iterated modalities [Sider] |
13708 | S5 is the strongest system, since it has the most valid formulas, because it is easy to be S5-valid [Sider] |
13712 | Epistemic accessibility is reflexive, and allows positive and negative introspection (KK and K¬K) [Sider] |
13714 | We can treat modal worlds as different times [Sider] |
13720 | Converse Barcan Formula: □∀αφ→∀α□φ [Sider] |
13718 | The Barcan Formula ∀x□Fx→□∀xFx may be a defect in modal logic [Sider] |
13723 | System B is needed to prove the Barcan Formula [Sider] |
13715 | You can employ intuitionist logic without intuitionism about mathematics [Sider] |
13678 | The most popular account of logical consequence is the semantic or model-theoretic one [Sider] |
13679 | Maybe logical consequence is more a matter of provability than of truth-preservation [Sider] |
13682 | Maybe logical consequence is impossibility of the premises being true and the consequent false [Sider] |
13680 | Maybe logical consequence is a primitive notion [Sider] |
13722 | A 'theorem' is an axiom, or the last line of a legitimate proof [Sider] |
13696 | When a variable is 'free' of the quantifier, the result seems incapable of truth or falsity [Sider] |
13700 | A 'total' function must always produce an output for a given domain [Sider] |
13703 | λ can treat 'is cold and hungry' as a single predicate [Sider] |
13688 | Good axioms should be indisputable logical truths [Sider] |
13687 | No assumptions in axiomatic proofs, so no conditional proof or reductio [Sider] |
13690 | Proof by induction 'on the length of the formula' deconstructs a formula into its accepted atoms [Sider] |
13691 | Induction has a 'base case', then an 'inductive hypothesis', and then the 'inductive step' [Sider] |
13685 | Natural deduction helpfully allows reasoning with assumptions [Sider] |
13686 | We can build proofs just from conclusions, rather than from plain formulae [Sider] |
13697 | Valuations in PC assign truth values to formulas relative to variable assignments [Sider] |
13684 | The semantical notion of a logical truth is validity, being true in all interpretations [Sider] |
13704 | It is hard to say which are the logical truths in modal logic, especially for iterated modal operators [Sider] |
13724 | In model theory, first define truth, then validity as truth in all models, and consequence as truth-preservation [Sider] |
13698 | In a complete logic you can avoid axiomatic proofs, by using models to show consequences [Sider] |
13699 | Compactness surprisingly says that no contradictions can emerge when the set goes infinite [Sider] |
13701 | A single second-order sentence validates all of arithmetic - but this can't be proved axiomatically [Sider] |
23783 | Change exists, it is causal, and it needs an explanation [Williams,NE] |
23784 | Processes don't begin or end; they just change direction unexpectedly [Williams,NE] |
23790 | Processes are either strings of short unchanging states, or continuous and unreducible events [Williams,NE] |
23786 | The status quo is part of what exists, and so needs metaphysical explanation [Williams,NE] |
23768 | A metaphysic is a set of wider explanations derived from a basic ontology [Williams,NE] |
23773 | Humeans say properties are passive, possibility is vast, laws are descriptions, causation is weak [Williams,NE] |
23779 | We shouldn't posit the existence of anything we have a word for [Williams,NE] |
13692 | A 'precisification' of a trivalent interpretation reduces it to a bivalent interpretation [Sider] |
13695 | Supervaluational logic is classical, except when it adds the 'Definitely' operator [Sider] |
13693 | A 'supervaluation' assigns further Ts and Fs, if they have been assigned in every precisification [Sider] |
13694 | We can 'sharpen' vague terms, and then define truth as true-on-all-sharpenings [Sider] |
13683 | A relation is a feature of multiple objects taken together [Sider] |
23775 | Powers are 'multi-track' if they can produce a variety of manifestations [Williams,NE] |
23780 | Every possible state of affairs is written into its originating powers [Williams,NE] |
23789 | Naming powers is unwise, because that it usually done by a single manifestation [Williams,NE] |
23771 | Fundamental physics describes everything in terms of powers [Williams,NE] |
23776 | Rather than pure powers or pure categoricals, I favour basics which are both at once [Williams,NE] |
23777 | Powers are more complicated than properties which are always on display [Williams,NE] |
23774 | There are basic powers, which underlie dispositions, potentialities, capacities etc [Williams,NE] |
23791 | Dispositions are just useful descriptions, which are explained by underlying powers [Williams,NE] |
23772 | If objects are property bundles, the properties need combining powers [Williams,NE] |
23788 | Four-Dimensional is Perdurantism (temporal parts), plus Eternalism [Williams,NE] |
13702 | The identity of indiscernibles is necessarily true, if being a member of some set counts as a property [Sider] |
13721 | 'Strong' necessity in all possible worlds; 'weak' necessity in the worlds where the relevant objects exist [Sider] |
13707 | Maybe metaphysical accessibility is intransitive, if a world in which I am a frog is impossible [Sider] |
13709 | Logical truths must be necessary if anything is [Sider] |
13716 | 'If B hadn't shot L someone else would have' if false; 'If B didn't shoot L, someone else did' is true [Sider] |
13717 | Transworld identity is not a problem in de dicto sentences, which needn't identify an individual [Sider] |
13719 | Barcan Formula problem: there might have been a ghost, despite nothing existing which could be a ghost [Sider] |
5961 | The soul gets its goodness from god, and its evil from previous existence. [Plato] |
283 | The question of whether or not to persuade comes before the science of persuasion [Plato] |
282 | Non-physical beauty can only be shown clearly by speech [Plato] |
281 | The arts produce good and beautiful things by preserving the mean [Plato] |
22559 | Democracy is the worst of good constitutions, but the best of bad constitutions [Plato, by Aristotle] |
23785 | Causation needs to explain stasis, as well as change [Williams,NE] |
23782 | Causation is the exercise of powers [Williams,NE] |
23787 | If causes and effects overlap, that makes changes impossible [Williams,NE] |
23778 | Powers contain lawlike features, pointing to possible future states [Williams,NE] |
279 | Only divine things can always stay the same, and bodies are not like that [Plato] |