9 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… |
| 11966 | If there are essential properties, how do you find out what they are? [Chisholm] |
| Full Idea: It seems to me that if Adam does have essential properties, there is no procedure at all for finding out what they are. | |
| From: Roderick Chisholm (Identity through Possible Worlds [1967], p.85) | |
| A reaction: My tentative suggestion is that the essential properties are those which explain the nature, power, function and role of Adam in the 'actual' world. Whatever possibilities he acquires, he had better retain the capacity to be the First Man. |
| 11965 | Could possible Adam gradually transform into Noah, and vice versa? [Chisholm] |
| Full Idea: If Adam lived for 931 years in a possible world, instead of his actual 930 years, ..then Adam and Noah could gradually exchange their ages and other properties...and we could trace Adam in a world back to the actual Noah, and vice versa. | |
| From: Roderick Chisholm (Identity through Possible Worlds [1967], p.81-2) | |
| A reaction: [very compressed] Chisholm was one of the first to raise this problem for possible worlds, though it had been Quine's objection to modal logic all along. Only Adam having essential properties seems to stop this slippery slope, says Chisholm. |
| 19691 | Unlike knowledge, you can achieve understanding through luck [Grimm] |
| Full Idea: It may be that understanding is compatible with luck, in a way that knowledge is not. | |
| From: Stephen R. Grimm (Understanding [2011], 3) | |
| A reaction: [He cites Kvanvig and Prichard] If so, then we cannot say that knowledge is a lesser type of understanding. If you ask a trusted person how a mechanism works, and they have a wild guess that is luckily right, you would then understand it. |
| 19690 | 'Grasping' a structure seems to be modal, because we must anticipate its behaviour [Grimm] |
| Full Idea: 'Graspng' a structure would seem to bring into play something like a modal sense or ability, not just to register how things are, but also to anticipate how certain elements of the system would behave. | |
| From: Stephen R. Grimm (Understanding [2011], 2) | |
| A reaction: In the case of the chronology of some historical events, talking of 'grasping' or 'understanding' seems wrong because the facts are static and invariant. That seems to support the present idea. But you might 'understand' a pattern if you can reproduce it. |
| 19692 | You may have 'weak' understanding, if by luck you can answer a set of 'why questions' [Grimm] |
| Full Idea: There may be a 'weak' sense of understanding, where all you need to do is to be able to answer 'why questions' successfully, where one might have come by this ability in a lucky way. | |
| From: Stephen R. Grimm (Understanding [2011], 3) | |
| A reaction: We can see this point (in Idea 19691), but the idea that one could come by true complex understanding of something by purely lucky means is a bit absurd. Surely you would get one or two why questions wrong? 100%, just by luck? |