83 ideas
4767 | Traditionally, rational beliefs are those which are justified by reasons [Psillos] |
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] |
13640 | Russell's paradox shows that there are classes which are not iterative sets [Shapiro] |
13654 | It is central to the iterative conception that membership is well-founded, with no infinite descending chains [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] |
13642 | Logic is the ideal for learning new propositions on the basis of others [Shapiro] |
13627 | There is no 'correct' logic for natural languages [Shapiro] |
13667 | Skolem and Gödel championed first-order, and Zermelo, Hilbert, and Bernays championed higher-order [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] |
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] |
13637 | If a logic is incomplete, its semantic consequence relation is not effective [Shapiro] |
13626 | Semantic consequence is ineffective in second-order logic [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] |
4810 | Valid deduction is monotonic - that is, it remains valid if further premises are added [Psillos] |
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] |
4768 | The 'epistemic fallacy' is inferring what does exist from what can be known to exist [Psillos] |
13638 | Properties are often seen as intensional; equiangular and equilateral are different, despite identity of objects [Shapiro] |
4808 | If we say where Mars was two months ago, we offer an explanation without a prediction [Psillos] |
4807 | A good barometer will predict a storm, but not explain it [Psillos] |
4811 | Induction (unlike deduction) is non-monotonic - it can be invalidated by new premises [Psillos] |
4812 | Explanation is either showing predictability, or showing necessity, or showing causal relations [Psillos] |
4802 | Just citing a cause does not enable us to understand an event; we also need a relevant law [Psillos] |
4804 | The 'covering law model' says only laws can explain the occurrence of single events [Psillos] |
4805 | If laws explain the length of a flagpole's shadow, then the shadow also explains the length of the pole [Psillos] |
4806 | An explanation can just be a 'causal story', without laws, as when I knock over some ink [Psillos] |
4395 | There are non-causal explanations, most typically mathematical explanations [Psillos] |
4404 | Maybe explanation is entirely relative to the interests and presuppositions of the questioner [Psillos] |
4803 | An explanation is the removal of the surprise caused by the event [Psillos] |
4769 | It is hard to analyse causation, if it is presupposed in our theory of the functioning of the mind [Psillos] |
4770 | Nothing is more usual than to apply to external bodies every internal sensation which they occasion [Psillos] |
467 | A virtue is a combination of intelligence, strength and luck [Ion] |
4399 | Causes clearly make a difference, are recipes for events, explain effects, and are evidence [Psillos] |
4400 | Theories of causation are based either on regularity, or on intrinsic relations of properties [Psillos] |
4403 | We can't base our account of causation on explanation, because it is the wrong way round [Psillos] |
4789 | Three divisions of causal theories: generalist/singularist, intrinsic/extrinsic, reductive/non-reductive [Psillos] |
4790 | If causation is 'intrinsic' it depends entirely on the properties and relations of the cause and effect [Psillos] |
4402 | Empiricists tried to reduce causation to explanation, which they reduced to logic-plus-a-law [Psillos] |
4774 | Counterfactual claims about causation imply that it is more than just regular succession [Psillos] |
4793 | "All gold cubes are smaller than one cubic mile" is a true universal generalisation, but not a law [Psillos] |
4397 | Regularity doesn't seem sufficient for causation [Psillos] |
4401 | It is not a law of nature that all the coins in my pocket are euros, though it is a regularity [Psillos] |
4792 | A Humean view of causation says it is regularities, and causal facts supervene on non-causal facts [Psillos] |
4801 | The regularity of a cock's crow is used to predict dawn, even though it doesn't cause it [Psillos] |
4796 | Laws are sets of regularities within a simple and strong coherent system of wider regularities [Psillos] |
4799 | Dispositional essentialism can't explain its key distinction between essential and non-essential properties [Psillos] |
4780 | In some counterfactuals, the counterfactual event happens later than its consequent [Psillos] |
4791 | Counterfactual theories say causes make a difference - if c hadn't occurred, then e wouldn't occur [Psillos] |