12 ideas
| 10163 | Propositional modal logic has been proved to be complete [Kripke, by Feferman/Feferman] |
| Full Idea: At the age of 19 Saul Kripke published a completeness proof of propositional modal logic. | |
| From: report of Saul A. Kripke (A Completeness Theorem in Modal Logic [1959]) by Feferman / Feferman - Alfred Tarski: life and logic Int V |
| 10760 | With possible worlds, S4 and S5 are sound and complete, but S1-S3 are not even sound [Kripke, by Rossberg] |
| Full Idea: Kripke gave a possible worlds semantics to a whole range of modal logics, and S4 and S5 turned out to be both sound and complete with this semantics. Hence more systems could be designed. S1-S3 failed in soundness, leading to 'impossible worlds'. | |
| From: report of Saul A. Kripke (A Completeness Theorem in Modal Logic [1959]) by Marcus Rossberg - First-order Logic, 2nd-order, Completeness §4 |
| 16189 | The variable domain approach to quantified modal logic invalidates the Barcan Formula [Kripke, by Simchen] |
| Full Idea: Kripke's variable domain approach to quantified modal logic famously invalidates the Barcan Formula. | |
| From: report of Saul A. Kripke (A Completeness Theorem in Modal Logic [1959]) by Ori Simchen - The Barcan Formula and Metaphysics §3 | |
| A reaction: [p.9 and p.16] In a single combined domain all the possibilia must be present, but with variable domains objects in remote domains may not exist in your local domain. BF is committed to those possible objects. |
| 15132 | The Barcan formulas fail in models with varying domains [Kripke, by Williamson] |
| Full Idea: Kripke showed that the Barcan formula ∀x□A⊃□∀xA and its converse fail in models which require varying domains. | |
| From: report of Saul A. Kripke (A Completeness Theorem in Modal Logic [1959]) by Timothy Williamson - Truthmakers and Converse Barcan Formula §1 | |
| A reaction: I think this is why I reject the Barcan formulas for metaphysics - because the domain of metaphysics should be seen as varying, since some objects are possible in some contexts and not in others. Hmm… |
| 1556 | By nature people are close to one another, but culture drives them apart [Hippias] |
| Full Idea: I regard you all as relatives - by nature, not by convention. By nature like is akin to like, but convention is a tyrant over humankind and often constrains people to act contrary to nature. | |
| From: Hippias (fragments/reports [c.430 BCE]), quoted by Plato - Protagoras 337c8 |
| 7127 | If men are good you should keep promises, but they aren't, so you needn't [Machiavelli] |
| Full Idea: If all men were good, promising-breaking would not be good, but because they are bad and do not keep their promises to you, you likewise do not have to keep yours to them. | |
| From: Niccolo Machiavelli (The Prince [1513], Ch.18) | |
| A reaction: A rather depressing proposal to get your promise-breaking in first, based on the pessimistic view that people cannot be improved. The subsequent history of ethics in Europe showed Machiavelli to be wrong. Gentlemen began to keep their word. |
| 6309 | The principle foundations of all states are good laws and good armies [Machiavelli] |
| Full Idea: The principle foundations of all states are good laws and good armies. | |
| From: Niccolo Machiavelli (The Prince [1513], Ch.11) | |
| A reaction: We may be wondering, since 1945, whether a good army is any longer essential, but it would be a foolish modern state which didn't at least form a strong alliance with a state which had a strong army. Fertile land is a huge benefit to a state. |
| 6305 | To retain a conquered state, wipe out the ruling family, and preserve everything else [Machiavelli] |
| Full Idea: If a ruler acquires a state and is determined to keep it, he observes two cautions: he wipes out the family of their long-established princes; and he does not change either their laws or their taxes; in a short time they will unite with his old princedom. | |
| From: Niccolo Machiavelli (The Prince [1513], Ch.3) | |
| A reaction: This nicely illustrates the firmness of purpose for which Machiavelli has become a byword. The question is whether Machiavelli had enough empirical evidence to support this induction. The British in India seem to have been successful without it. |
| 6308 | A sensible conqueror does all his harmful deeds immediately, because people soon forget [Machiavelli] |
| Full Idea: A prudent conqueror makes a list of all the harmful deeds he must do, and does them all at once, so that he need not repeat them every day, which then makes men feel secure, and gains their support by treating them well. | |
| From: Niccolo Machiavelli (The Prince [1513], Ch.8) | |
| A reaction: This might work for a new government in a democracy, or a new boss in a business. It sounds horribly true; dreadful deeds done a long time ago can be completely forgotten, as when reformed criminals become celebrities. |
| 6306 | People are vengeful, so be generous to them, or destroy them [Machiavelli] |
| Full Idea: Men should be either treated generously or destroyed, because they take revenge for slight injuries. | |
| From: Niccolo Machiavelli (The Prince [1513], Ch.3) | |
| A reaction: This sounds like good advice, and works quite well in school teaching too. It seems like advice drawn from the growth of the Roman Empire, rather than from dealing with sophisticated and educated people. |
| 6307 | A desire to conquer, and men who do it, are always praised, or not blamed [Machiavelli] |
| Full Idea: It is very natural and normal to wish to conquer, and when men do it who can, they always will be praised, or not blamed. | |
| From: Niccolo Machiavelli (The Prince [1513], Ch.3) | |
| A reaction: This view seems shocking to us, but it seems to me that this was a widely held view up until the time of Nietzsche, but came to a swift end with the invention of the machine gun in about 1885, followed by the heavy bomber and atomic bomb. |
| 7486 | Machiavelli emancipated politics from religion [Machiavelli, by Watson] |
| Full Idea: Machiavelli emancipated politics from religion. | |
| From: report of Niccolo Machiavelli (The Prince [1513]) by Peter Watson - Ideas Ch.24 | |
| A reaction: Interestingly, he seems to have done it by saying that ideals are irrelevant to politics, but gradually secular ideals crept back in (sometimes disastrously). A balance needs to be struck on idealism. |