90 ideas
| 19767 | Reason leads to prudent selfishness, which overrules natural compassion [Rousseau] |
| 10835 | True sentences says the appropriate descriptive thing on the appropriate demonstrative occasion [Austin,JL] |
| 10836 | Correspondence theorists shouldn't think that a country has just one accurate map [Austin,JL] |
| 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] |
| 19757 | No one would bother to reason, and try to know things, without a desire for enjoyment [Rousseau] |
| 19760 | General ideas are purely intellectual; imagining them is immediately particular [Rousseau] |
| 19759 | Only words can introduce general ideas into the mind [Rousseau] |
| 19758 | Language may aid thinking, but powerful thought was needed to produce language [Rousseau] |
| 19773 | Without love, what use is beauty? [Rousseau] |
| 19769 | Rational morality is OK for brainy people, but ordinary life can't rely on that [Rousseau] |
| 19752 | If we should not mistreat humans, it is mainly because of sentience, not rationality [Rousseau] |
| 19768 | The better Golden Rule is 'do good for yourself without harming others' [Rousseau] |
| 19766 | The fact that we weep (e.g. in theatres) shows that we are naturally compassionate [Rousseau] |
| 19756 | Humans are less distinguished from other animals by understanding, than by being free agents [Rousseau] |
| 19755 | Most human ills are self-inflicted; the simple, solitary, regular natural life is good [Rousseau] |
| 19762 | Is language a pre-requisite for society, or might it emerge afterwards? [Rousseau] |
| 19763 | I doubt whether a savage person ever complains of life, or considers suicide [Rousseau] |
| 19778 | Leisure led to envy, inequality, vice and revenge, which we now see in savages [Rousseau] |
| 19779 | Primitive man was very gentle [Rousseau] |
| 19751 | Our two starting principles are concern for self-interest, and compassion for others [Rousseau] |
| 19765 | Savages avoid evil because they are calm, and never think of it (not because they know goodness) [Rousseau] |
| 19771 | Savage men quietly pursue desires, without the havoc of modern frenzied imagination [Rousseau] |
| 19774 | A savage can steal fruit or a home, but there is no means of achieving obedience [Rousseau] |
| 19772 | In a state of nature people are much more equal; it is society which increases inequalities [Rousseau] |
| 19789 | It is against nature for children to rule old men, fools to rule the wise, and the rich to hog resources [Rousseau] |
| 19787 | People accept the right to be commanded, because they themselves wish to command [Rousseau] |
| 19780 | We seem to have made individual progress since savagery, but actually the species has decayed [Rousseau] |
| 19747 | Revolutionaries usually confuse liberty with total freedom, and end up with heavier chains [Rousseau] |
| 19748 | Plebiscites are bad, because they exclude the leaders from crucial decisions [Rousseau] |
| 19749 | In a direct democracy, only the leaders should be able to propose new laws [Rousseau] |
| 19784 | Enslaved peoples often boast of their condition, calling it a state of 'peace' [Rousseau] |
| 19785 | If the child of a slave woman is born a slave, then a man is not born a man [Rousseau] |
| 19775 | People must be made dependent before they can be enslaved [Rousseau] |
| 19746 | Like rich food, liberty can ruin people who are too weak to cope with it [Rousseau] |
| 19786 | Three stages of the state produce inequalities of wealth, power, and enslavement [Rousseau] |
| 19788 | The pleasure of wealth and power is largely seeing others deprived of them [Rousseau] |
| 19777 | Persuading other people that some land was 'owned' was the beginning of society [Rousseau] |
| 19782 | What else could property arise from, but the labour people add to it? [Rousseau] |
| 19781 | Land cultivation led to a general right of ownership, administered justly [Rousseau] |
| 19754 | If we have a natural right to property, what exactly does 'belonging to' mean? [Rousseau] |
| 19750 | Writers just propose natural law as the likely useful agreements among people [Rousseau] |
| 19770 | Primitive people simply redressed the evil caused by violence, without thought of punishing [Rousseau] |
| 19783 | A state of war remains after a conquest, if the losers don't accept the winners [Rousseau] |
| 19753 | Both men and animals are sentient, which should give the latter the right not to be mistreated [Rousseau] |
| 19761 | Men started with too few particular names, but later had too few natural kind names [Rousseau] |
| 19776 | Small uninterrupted causes can have big effects [Rousseau] |