30 ideas
1597 | Thales was the first western thinker to believe the arché was intelligible [Roochnik on Thales] |
10476 | The idea that groups of concepts could be 'implicitly defined' was abandoned [Hodges,W] |
10282 | Logic is the study of sound argument, or of certain artificial languages (or applying the latter to the former) [Hodges,W] |
10478 | Since first-order languages are complete, |= and |- have the same meaning [Hodges,W] |
10477 | |= in model-theory means 'logical consequence' - it holds in all models [Hodges,W] |
10283 | A formula needs an 'interpretation' of its constants, and a 'valuation' of its variables [Hodges,W] |
10284 | There are three different standard presentations of semantics [Hodges,W] |
10285 | I |= φ means that the formula φ is true in the interpretation I [Hodges,W] |
10474 | |= should be read as 'is a model for' or 'satisfies' [Hodges,W] |
10473 | Model theory studies formal or natural language-interpretation using set-theory [Hodges,W] |
10475 | A 'structure' is an interpretation specifying objects and classes of quantification [Hodges,W] |
10481 | Models in model theory are structures, not sets of descriptions [Hodges,W] |
10288 | Down Löwenheim-Skolem: if a countable language has a consistent theory, that has a countable model [Hodges,W] |
10289 | Up Löwenheim-Skolem: if infinite models, then arbitrarily large models [Hodges,W] |
10287 | If a first-order theory entails a sentence, there is a finite subset of the theory which entails it [Hodges,W] |
10480 | First-order logic can't discriminate between one infinite cardinal and another [Hodges,W] |
10286 | A 'set' is a mathematically well-behaved class [Hodges,W] |
3013 | Nothing is stronger than necessity, which rules everything [Thales, by Diog. Laertius] |
7127 | If men are good you should keep promises, but they aren't, so you needn't [Machiavelli] |
6309 | The principle foundations of all states are good laws and good armies [Machiavelli] |
6306 | People are vengeful, so be generous to them, or destroy them [Machiavelli] |
6305 | To retain a conquered state, wipe out the ruling family, and preserve everything else [Machiavelli] |
6308 | A sensible conqueror does all his harmful deeds immediately, because people soon forget [Machiavelli] |
6307 | A desire to conquer, and men who do it, are always praised, or not blamed [Machiavelli] |
7486 | Machiavelli emancipated politics from religion [Machiavelli, by Watson] |
19813 | All legislators invoke God in support of extraordinary laws, because their justification is not obvious [Machiavelli] |
7126 | Rulers should preserve the foundations of religion, to ensure good behaviour and unity [Machiavelli] |
1494 | Thales said water is the first principle, perhaps from observing that food is moist [Thales, by Aristotle] |
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] |