79 ideas
| 19917 | Without reason and human help, human life is misery [Spinoza] |
| 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] |
| 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] |
| 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] |
| 19922 | People are only free if they are guided entirely by reason [Spinoza] |
| 7903 | The six perfections are giving, morality, patience, vigour, meditation, and wisdom [Nagarjuna] |
| 19935 | Peoples are created by individuals, not by nature, and only distinguished by language and law [Spinoza] |
| 19914 | In nature everything has an absolute right to do anything it is capable of doing [Spinoza] |
| 19915 | Natural rights are determined by desire and power, not by reason [Spinoza] |
| 7487 | Society exists to extend human awareness [Spinoza, by Watson] |
| 19943 | The state aims to allow personal development, so its main purpose is freedom [Spinoza] |
| 19930 | Sovereignty must include the power to make people submit to it [Spinoza] |
| 19936 | Kings tend to fight wars for glory, rather than for peace and liberty [Spinoza] |
| 19937 | Monarchs are always proud, and can't back down [Spinoza] |
| 19940 | Deposing a monarch is dangerous, because the people are used to royal authority [Spinoza] |
| 19931 | Every state is more frightened of its own citizens than of external enemies [Spinoza] |
| 19920 | Democracy is a legitimate gathering of people who do whatever they can do [Spinoza] |
| 19933 | If religion is law, then piety is justice, impiety is crime, and non-believers must leave [Spinoza] |
| 19938 | Allowing religious ministers any control of the state is bad for both parties [Spinoza] |
| 19923 | Slavery is not just obedience, but acting only in the interests of the master [Spinoza] |
| 19939 | Government is oppressive if opinions can be crimes, because people can't give them up [Spinoza] |
| 19944 | Without liberty of thought there is no trust in the state, and corruption follows [Spinoza] |
| 19942 | Treason may be committed as much by words as by deeds [Spinoza] |
| 19924 | The freest state is a rational one, where people can submit themselves to reason [Spinoza] |
| 7827 | Spinoza wanted democracy based on individual rights, and is thus the first modern political philosopher [Stewart,M on Spinoza] |
| 19926 | The sovereignty has absolute power over citizens [Spinoza] |
| 19918 | Forming a society meant following reason, and giving up dangerous appetites and mutual harm [Spinoza] |
| 19919 | People only give up their rights, and keep promises, if they hope for some greater good [Spinoza] |
| 19921 | Once you have given up your rights, there is no going back [Spinoza] |
| 19925 | In democracy we don't abandon our rights, but transfer them to the majority of us [Spinoza] |
| 19928 | No one, in giving up their power and right, ceases to be a human being [Spinoza] |
| 19929 | Everyone who gives up their rights must fear the recipients of them [Spinoza] |
| 19932 | The early Hebrews, following Moses, gave up their rights to God alone [Spinoza] |
| 19916 | The order of nature does not prohibit anything, and allows whatever appetite produces [Spinoza] |
| 19927 | State and religious law can clash, so the state must make decisions about religion [Spinoza] |
| 19934 | Hebrews were very hostile to other states, who had not given up their rights to God [Spinoza] |
| 4300 | The Bible has nothing in common with reasoning and philosophy [Spinoza] |