87 ideas
1597 | Thales was the first western thinker to believe the arché was intelligible [Roochnik on Thales] |
15801 | Many philosophers aim to understand metaphysics by studying ourselves [Chisholm] |
15802 | I use variables to show that each item remains the same entity throughout [Chisholm] |
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] |
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] |
15832 | Events are states of affairs that occur at certain places and times [Chisholm] |
15829 | The mark of a state of affairs is that it is capable of being accepted [Chisholm] |
15809 | A state of affairs pertains to a thing if it implies that it has some property [Chisholm] |
15828 | I propose that events and propositions are two types of states of affairs [Chisholm] |
15827 | Some properties, such as 'being a widow', can be seen as 'rooted outside the time they are had' [Chisholm] |
15830 | Some properties can never be had, like being a round square [Chisholm] |
15804 | If some dogs are brown, that entails the properties of 'being brown' and 'being canine' [Chisholm] |
13638 | Properties are often seen as intensional; equiangular and equilateral are different, despite identity of objects [Shapiro] |
15810 | Maybe we can only individuate things by relating them to ourselves [Chisholm] |
15805 | Being the tallest man is an 'individual concept', but not a haecceity [Chisholm] |
15807 | A haecceity is a property had necessarily, and strictly confined to one entity [Chisholm] |
15814 | A peach is sweet and fuzzy, but it doesn't 'have' those qualities [Chisholm] |
12852 | If x is ever part of y, then y is necessarily such that x is part of y at any time that y exists [Chisholm, by Simons] |
15808 | A traditional individual essence includes all of a thing's necessary characteristics [Chisholm] |
12851 | Intermittence is seen in a toy fort, which is dismantled then rebuilt with the same bricks [Chisholm, by Simons] |
15806 | The property of being identical with me is an individual concept [Chisholm] |
15826 | There is 'loose' identity between things if their properties, or truths about them, might differ [Chisholm] |
3013 | Nothing is stronger than necessity, which rules everything [Thales, by Diog. Laertius] |
15819 | Do sense-data have structure, location, weight, and constituting matter? [Chisholm] |
15816 | 'I feel depressed' is more like 'he runs slowly' than like 'he has a red book' [Chisholm] |
15817 | If we can say a man senses 'redly', why not also 'rectangularly'? [Chisholm] |
15818 | So called 'sense-data' are best seen as 'modifications' of the person experiencing them [Chisholm] |
15831 | Explanations have states of affairs as their objects [Chisholm] |
15811 | I am picked out uniquely by my individual essence, which is 'being identical with myself' [Chisholm] |
15815 | Sartre says the ego is 'opaque'; I prefer to say that it is 'transparent' [Chisholm] |
15813 | People use 'I' to refer to themselves, with the meaning of their own individual essence [Chisholm] |
15803 | Bad theories of the self see it as abstract, or as a bundle, or as a process [Chisholm] |
15821 | Determinism claims that every event has a sufficient causal pre-condition [Chisholm] |
15824 | There are mere omissions (through ignorance, perhaps), and people can 'commit an omission' [Chisholm] |
15822 | The concept of physical necessity is basic to both causation, and to the concept of nature [Chisholm] |
1494 | Thales said water is the first principle, perhaps from observing that food is moist [Thales, by Aristotle] |
15823 | Some propose a distinct 'agent causation', as well as 'event causation' [Chisholm] |
15820 | A 'law of nature' is just something which is physically necessary [Chisholm] |
1713 | Thales must have thought soul causes movement, since he thought magnets have soul [Thales, by Aristotle] |
1742 | Thales said the gods know our wrong thoughts as well as our evil actions [Thales, by Diog. Laertius] |