95 ideas
| 19767 | Reason leads to prudent selfishness, which overrules natural compassion [Rousseau] |
| 13634 | Satisfaction is 'truth in a model', which is a model of 'truth' [Shapiro] |
| 13643 | Aristotelian logic is complete [Shapiro] |
| 13651 | A set is 'transitive' if contains every member of each of its members [Shapiro] |
| 13647 | Choice is essential for proving downward Löwenheim-Skolem [Shapiro] |
| 13631 | Are sets part of logic, or part of mathematics? [Shapiro] |
| 13654 | It is central to the iterative conception that membership is well-founded, with no infinite descending chains [Shapiro] |
| 13640 | Russell's paradox shows that there are classes which are not iterative sets [Shapiro] |
| 13666 | Iterative sets are not Boolean; the complement of an iterative set is not an iterative sets [Shapiro] |
| 13653 | 'Well-ordering' of a set is an irreflexive, transitive, and binary relation with a least element [Shapiro] |
| 13627 | There is no 'correct' logic for natural languages [Shapiro] |
| 13642 | Logic is the ideal for learning new propositions on the basis of others [Shapiro] |
| 13668 | Bernays (1918) formulated and proved the completeness of propositional logic [Shapiro] |
| 13669 | Can one develop set theory first, then derive numbers, or are numbers more basic? [Shapiro] |
| 13667 | Skolem and Gödel championed first-order, and Zermelo, Hilbert, and Bernays championed higher-order [Shapiro] |
| 13662 | First-order logic was an afterthought in the development of modern logic [Shapiro] |
| 13624 | The 'triumph' of first-order logic may be related to logicism and the Hilbert programme, which failed [Shapiro] |
| 13660 | Maybe compactness, semantic effectiveness, and the Löwenheim-Skolem properties are desirable [Shapiro] |
| 13673 | The notion of finitude is actually built into first-order languages [Shapiro] |
| 15944 | Second-order logic is better than set theory, since it only adds relations and operations, and nothing else [Shapiro, by Lavine] |
| 13629 | Broad standard semantics, or Henkin semantics with a subclass, or many-sorted first-order semantics? [Shapiro] |
| 13650 | Henkin semantics has separate variables ranging over the relations and over the functions [Shapiro] |
| 13645 | In standard semantics for second-order logic, a single domain fixes the ranges for the variables [Shapiro] |
| 13649 | Completeness, Compactness and Löwenheim-Skolem fail in second-order standard semantics [Shapiro] |
| 13626 | Semantic consequence is ineffective in second-order logic [Shapiro] |
| 13637 | If a logic is incomplete, its semantic consequence relation is not effective [Shapiro] |
| 13632 | Finding the logical form of a sentence is difficult, and there are no criteria of correctness [Shapiro] |
| 13674 | We might reduce ontology by using truth of sentences and terms, instead of using objects satisfying models [Shapiro] |
| 13633 | 'Satisfaction' is a function from models, assignments, and formulas to {true,false} [Shapiro] |
| 13644 | Semantics for models uses set-theory [Shapiro] |
| 13636 | An axiomatization is 'categorical' if its models are isomorphic, so there is really only one interpretation [Shapiro] |
| 13670 | Categoricity can't be reached in a first-order language [Shapiro] |
| 13658 | Downward Löwenheim-Skolem: each satisfiable countable set always has countable models [Shapiro] |
| 13659 | Upward Löwenheim-Skolem: each infinite model has infinite models of all sizes [Shapiro] |
| 13648 | The Löwenheim-Skolem theorems show an explosion of infinite models, so 1st-order is useless for infinity [Shapiro] |
| 13675 | Substitutional semantics only has countably many terms, so Upward Löwenheim-Skolem trivially fails [Shapiro] |
| 13635 | 'Weakly sound' if every theorem is a logical truth; 'sound' if every deduction is a semantic consequence [Shapiro] |
| 13628 | We can live well without completeness in logic [Shapiro] |
| 13630 | Non-compactness is a strength of second-order logic, enabling characterisation of infinite structures [Shapiro] |
| 13646 | Compactness is derived from soundness and completeness [Shapiro] |
| 13661 | A language is 'semantically effective' if its logical truths are recursively enumerable [Shapiro] |
| 13641 | Complex numbers can be defined as reals, which are defined as rationals, then integers, then naturals [Shapiro] |
| 13676 | Only higher-order languages can specify that 0,1,2,... are all the natural numbers that there are [Shapiro] |
| 13677 | Natural numbers are the finite ordinals, and integers are equivalence classes of pairs of finite ordinals [Shapiro] |
| 13652 | The 'continuum' is the cardinality of the powerset of a denumerably infinite set [Shapiro] |
| 13657 | First-order arithmetic can't even represent basic number theory [Shapiro] |
| 13656 | Some sets of natural numbers are definable in set-theory but not in arithmetic [Shapiro] |
| 13664 | Logicism is distinctive in seeking a universal language, and denying that logic is a series of abstractions [Shapiro] |
| 13625 | Mathematics and logic have no border, and logic must involve mathematics and its ontology [Shapiro] |
| 13663 | Some reject formal properties if they are not defined, or defined impredicatively [Shapiro] |
| 13638 | Properties are often seen as intensional; equiangular and equilateral are different, despite identity of objects [Shapiro] |
| 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] |
| 19775 | People must be made dependent before they can be enslaved [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] |
| 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] |
| 9111 | God is not wise, but more-than-wise; God is not good, but more-than-good [William of Ockham] |
| 9112 | We could never form a concept of God's wisdom if we couldn't abstract it from creatures [William of Ockham] |