53 ideas
| 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] |
| 13520 | A 'tautology' must include connectives [Wolf,RS] |
| 13524 | Deduction Theorem: T∪{P}|-Q, then T|-(P→Q), which justifies Conditional Proof [Wolf,RS] |
| 13521 | Universal Specification: ∀xP(x) implies P(t). True for all? Then true for an instance [Wolf,RS] |
| 13522 | Universal Generalization: If we prove P(x) with no special assumptions, we can conclude ∀xP(x) [Wolf,RS] |
| 13523 | Existential Generalization (or 'proof by example'): if we can say P(t), then we can say something is P [Wolf,RS] |
| 13529 | Empty Set: ∃x∀y ¬(y∈x). The unique empty set exists [Wolf,RS] |
| 13526 | Comprehension Axiom: if a collection is clearly specified, it is a set [Wolf,RS] |
| 13534 | In first-order logic syntactic and semantic consequence (|- and |=) nicely coincide [Wolf,RS] |
| 13535 | First-order logic is weakly complete (valid sentences are provable); we can't prove every sentence or its negation [Wolf,RS] |
| 13519 | Model theory uses sets to show that mathematical deduction fits mathematical truth [Wolf,RS] |
| 13531 | Model theory reveals the structures of mathematics [Wolf,RS] |
| 13532 | Model theory 'structures' have a 'universe', some 'relations', some 'functions', and some 'constants' [Wolf,RS] |
| 13533 | First-order model theory rests on completeness, compactness, and the Löwenheim-Skolem-Tarski theorem [Wolf,RS] |
| 13537 | An 'isomorphism' is a bijection that preserves all structural components [Wolf,RS] |
| 13539 | The LST Theorem is a serious limitation of first-order logic [Wolf,RS] |
| 13538 | If a theory is complete, only a more powerful language can strengthen it [Wolf,RS] |
| 13525 | Most deductive logic (unlike ordinary reasoning) is 'monotonic' - we don't retract after new givens [Wolf,RS] |
| 13530 | An ordinal is an equivalence class of well-orderings, or a transitive set whose members are transitive [Wolf,RS] |
| 13518 | Modern mathematics has unified all of its objects within set theory [Wolf,RS] |
| 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] |
| 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] |
| 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] |
| 13304 | Learned men gain more in one day than others do in a lifetime [Posidonius] |
| 15822 | The concept of physical necessity is basic to both causation, and to the concept of nature [Chisholm] |
| 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] |
| 20820 | Time is an interval of motion, or the measure of speed [Posidonius, by Stobaeus] |