86 ideas
421 | Men who love wisdom must be inquirers into very many things indeed [Heraclitus] |
1491 | Everyone has the potential for self-knowledge and sound thinking [Heraclitus] |
5863 | Reason is eternal, but men are foolish [Heraclitus] |
414 | Logos is common to all, but most people live as if they have a private understanding [Heraclitus] |
416 | Beautiful harmony comes from things that are in opposition to one another [Heraclitus] |
425 | A thing can have opposing tensions but be in harmony, like a lyre [Heraclitus] |
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] |
1312 | If everything is and isn't then everything is true, and a midway between true and false makes everything false [Aristotle on Heraclitus] |
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] |
15658 | The hidden harmony is stronger than the visible [Heraclitus] |
13782 | Everything gives way, and nothing stands fast [Heraclitus] |
11853 | A mixed drink separates if it is not stirred [Heraclitus] |
427 | It is not possible to step twice into the same river [Heraclitus] |
11091 | You can bathe in the same river twice, but not in the same river stage [Quine on Heraclitus] |
2064 | If flux is continuous, then lack of change can't be a property, so everything changes in every possible way [Plato on Heraclitus] |
430 | Senses are no use if the soul is corrupt [Heraclitus] |
1500 | When we sleep, reason closes down as the senses do [Heraclitus, by Sext.Empiricus] |
417 | Donkeys prefer chaff to gold [Heraclitus] |
426 | Sea water is life-giving for fish, but not for people [Heraclitus] |
431 | Health, feeding and rest are only made good by disease, hunger and weariness [Heraclitus] |
429 | To God (though not to humans) all things are beautiful and good and just [Heraclitus] |
12294 | Good and evil are the same thing [Heraclitus, by Aristotle] |
419 | If one does not hope, one will not find the unhoped-for, since nothing leads to it [Heraclitus] |
415 | If happiness is bodily pleasure, then oxen are happy when they have vetch to eat [Heraclitus] |
5155 | It is hard to fight against emotion, but harder still to fight against pleasure [Heraclitus] |
433 | For man character is destiny [Heraclitus] |
422 | The people should fight for the law as if for their city-wall [Heraclitus] |
614 | Heraclitus said sometimes everything becomes fire [Heraclitus, by Aristotle] |
424 | Reason tells us that all things are one [Heraclitus] |
5096 | Heraclitus says that at some time everything becomes fire [Heraclitus, by Aristotle] |
17539 | The sayings of Heraclitus are still correct, if we replace 'fire' with 'energy' [Heraclitus, by Heisenberg] |
3054 | Heraclitus said fire could be transformed to create the other lower elements [Heraclitus, by Diog. Laertius] |
15660 | Logos is the source of everything, and my theories separate and explain each nature [Heraclitus] |
12269 | All things are in a state of motion [Heraclitus, by Aristotle] |
420 | The cosmos is eternal not created, and is an ever-living and changing fire [Heraclitus] |
1499 | Heraclitus says intelligence draws on divine reason [Heraclitus, by Sext.Empiricus] |
15659 | Purifying yourself with blood is as crazy as using mud to wash off mud [Heraclitus] |
1501 | In their ignorance people pray to statues, which is like talking to a house [Heraclitus] |