79 ideas
13634 | Satisfaction is 'truth in a model', which is a model of 'truth' [Shapiro] |
13643 | Aristotelian logic is complete [Shapiro] |
15879 | The Square of Opposition has two contradictory pairs, one contrary pair, and one sub-contrary pair [Harré] |
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] |
15891 | Traditional quantifiers combine ordinary language generality and ontology assumptions [Harré] |
13674 | We might reduce ontology by using truth of sentences and terms, instead of using objects satisfying models [Shapiro] |
15878 | Some quantifiers, such as 'any', rule out any notion of order within their range [Harré] |
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] |
15874 | Scientific properties are not observed qualities, but the dispositions which create them [Harré] |
13638 | Properties are often seen as intensional; equiangular and equilateral are different, despite identity of objects [Shapiro] |
15884 | Laws of nature remain the same through any conditions, if the underlying mechanisms are unchanged [Harré] |
15880 | In physical sciences particular observations are ordered, but in biology only the classes are ordered [Harré] |
15869 | Reports of experiments eliminate the experimenter, and present results as the behaviour of nature [Harré] |
15881 | We can save laws from counter-instances by treating the latter as analytic definitions [Harré] |
15882 | Since there are three different dimensions for generalising laws, no one system of logic can cover them [Harré] |
15888 | The grue problem shows that natural kinds are central to science [Harré] |
15887 | 'Grue' introduces a new causal hypothesis - that emeralds can change colour [Harré] |
15889 | It is because ravens are birds that their species and their colour might be connected [Harré] |
15890 | Non-black non-ravens just aren't part of the presuppositions of 'all ravens are black' [Harré] |
15885 | The necessity of Newton's First Law derives from the nature of material things, not from a mechanism [Harré] |
15868 | Idealisation idealises all of a thing's properties, but abstraction leaves some of them out [Harré] |
1748 | Archelaus was the first person to say that the universe is boundless [Archelaus, by Diog. Laertius] |
15886 | Science rests on the principle that nature is a hierarchy of natural kinds [Harré] |
15864 | Classification is just as important as laws in natural science [Harré] |
15865 | Newton's First Law cannot be demonstrated experimentally, as that needs absence of external forces [Harré] |
15862 | Laws can come from data, from theory, from imagination and concepts, or from procedures [Harré] |
15870 | Are laws of nature about events, or types and universals, or dispositions, or all three? [Harré] |
15871 | Are laws about what has or might happen, or do they also cover all the possibilities? [Harré] |
15876 | Maybe laws of nature are just relations between properties? [Harré] |
15860 | We take it that only necessary happenings could be laws [Harré] |
15867 | Laws describe abstract idealisations, not the actual mess of nature [Harré] |
15872 | Must laws of nature be universal, or could they be local? [Harré] |
15892 | Laws of nature state necessary connections of things, events and properties, based on models of mechanisms [Harré] |
15875 | In counterfactuals we keep substances constant, and imagine new situations for them [Harré] |
5989 | Archelaus said life began in a primeval slime [Archelaus, by Schofield] |