7 ideas
| 9879 | NF has no models, but just blocks the comprehension axiom, to avoid contradictions [Quine, by Dummett] |
| Full Idea: Quine's New Foundations system of set theory, devised with no model in mind, but on the basis of a hunch that a purely formal restriction on the comprehension axiom would block all contradictions. | |
| From: report of Willard Quine (New Foundations for Mathematical Logic [1937]) by Michael Dummett - Frege philosophy of mathematics Ch.18 | |
| A reaction: The point is that Quine (who had an ontological preference for 'desert landscapes') attempted to do without an ontological commitment to objects (and their subsequent models), with a purely formal system. Quine's NF is not now highly regarded. |
| 9390 | Logic guides thinking, but it isn't a substitute for it [Rumfitt] |
| Full Idea: Logic is part of a normative theory of thinking, not a substitute for thinking. | |
| From: Ian Rumfitt (The Logic of Boundaryless Concepts [2007], p.13) | |
| A reaction: There is some sort of logicians' dream, going back to Leibniz, of a reasoning engine, which accepts propositions and outputs inferences. I agree with this idea. People who excel at logic are often, it seems to me, modest at philosophy. |
| 13174 | A piece of flint contains something resembling perceptions and appetites [Leibniz] |
| Full Idea: I don't say that bodies like flint, which are commonly called inanimate, have perceptions and appetition; rather they have something of that sort in them, like worms are in cheese. | |
| From: Gottfried Leibniz (Letters to Johann Bernoulli [1699], 1698.12.17) | |
| A reaction: Leibniz is caricatured as thinking that stones are full of little active minds, but he nearly always says that what he is proposing is 'like' or 'analogous to' that. His only real point is that nature is active, as seen in the appetites of animals. |
| 13175 | Entelechies are analogous to souls, as other minds are analogous to our own minds [Leibniz] |
| Full Idea: Just as we somehow conceive other souls and intelligences on analogy with our own souls, I wanted whatever other primitive entelechies there may be remote from our senses to be conceived on analogy with souls. They are not conceived perfectly. | |
| From: Gottfried Leibniz (Letters to Johann Bernoulli [1699], 1698.12.17) | |
| A reaction: This is the clearest evidence I can find that Leibniz does not think of monads as actually being souls. He is struggling to explain their active character. Garber thinks that Leibniz hasn't arrived at proper monads at this date. |
| 9389 | Vague membership of sets is possible if the set is defined by its concept, not its members [Rumfitt] |
| Full Idea: Vagueness in respect of membership is consistency with determinacy of the set's identity, so long as a set's identity is taken to consist, not in its having such-and-such members, but in its being the extension of a concept. | |
| From: Ian Rumfitt (The Logic of Boundaryless Concepts [2007], p.5) | |
| A reaction: I find this view of sets much more appealing than the one that identifies a set with its members. The empty set is less of a problem, as well as non-existents. Logicians prefer the extensional view because it is tidy. |
| 13172 | What we cannot imagine may still exist [Leibniz] |
| Full Idea: It does not follow that what we can't imagine does not exist. | |
| From: Gottfried Leibniz (Letters to Johann Bernoulli [1699], 1698.11.18) | |
| A reaction: This just establishes the common sense end of the debate - that you cannot just use your imagination as the final authority on what exists, or what is possible. |
| 13173 | Death is just the contraction of an animal [Leibniz] |
| Full Idea: Death is nothing but the contraction of an animal, just as generation is nothing but its unfolding. | |
| From: Gottfried Leibniz (Letters to Johann Bernoulli [1699], 1698.11.18) | |
| A reaction: This is possibly the most bizarre view that I have found in Leibniz. He seemed to thing that if you burnt an animal on a bonfire, some little atom of life would remain among the ashes. I can't see why he would believe such a thing. |