35 ideas
13985 | A true proposition seems true of one fact, but a false proposition seems true of nothing at all. [Ryle] |
13984 | Two maps might correspond to one another, but they are only 'true' of the country they show [Ryle] |
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] |
13979 | Logic studies consequence, compatibility, contradiction, corroboration, necessitation, grounding.... [Ryle] |
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] |
13988 | Many sentences do not state facts, but there are no facts which could not be stated [Ryle] |
13983 | Representation assumes you know the ideas, and the reality, and the relation between the two [Ryle] |
13980 | If you like judgments and reject propositions, what are the relata of incoherence in a judgment? [Ryle] |
13978 | Husserl and Meinong wanted objective Meanings and Propositions, as subject-matter for Logic [Ryle] |
13977 | When I utter a sentence, listeners grasp both my meaning and my state of mind [Ryle] |
13976 | 'Propositions' name what is thought, because 'thoughts' and 'judgments' are too ambiguous [Ryle] |
13981 | Several people can believe one thing, or make the same mistake, or share one delusion [Ryle] |
13987 | We may think in French, but we don't know or believe in French [Ryle] |
13989 | There are no propositions; they are just sentences, used for thinking, which link to facts in a certain way [Ryle] |
13982 | If we accept true propositions, it is hard to reject false ones, and even nonsensical ones [Ryle] |
4055 | It isn't obviously wicked to destroy a potential human being (e.g. an ununited egg and sperm) [Lockwood] |
4056 | If the soul is held to leave the body at brain-death, it should arrive at the time of brain-creation [Lockwood] |
4054 | I may exist before I become a person, just as I exist before I become an adult [Lockwood] |