14 ideas
| 15527 | Defining terms either enables elimination, or shows that they don't require elimination [Lewis] |
| Full Idea: To define theoretical terms might be to show how to do without them, but it is better to say that it shows there is no good reason to want to do without them. | |
| From: David Lewis (How to Define Theoretical Terms [1970], Intro) |
| 1507 | We don't have time for infinite quantity, but we do for infinite divisibility, because time is also divisible [Aristotle on Zeno of Elea] |
| Full Idea: Although it is impossible to make contact in a finite time with things that are infinite in quantity, it is possible to do so with things that are infinitely divisible, since the time itself is also infinite in this way. | |
| From: comment on Zeno (Elea) (fragments/reports [c.450 BCE], A25) by Aristotle - Physics 233a21 |
| 5109 | The fast runner must always reach the point from which the slower runner started [Zeno of Elea, by Aristotle] |
| Full Idea: Zeno's so-called 'Achilles' claims that the slowest runner will never be caught by the fastest runner, because the one behind has first to reach the point from which the one in front started, and so the slower one is bound always to be in front. | |
| From: report of Zeno (Elea) (fragments/reports [c.450 BCE]) by Aristotle - Physics 239b14 | |
| A reaction: The point is that the slower runner will always have moved on when the faster runner catches up with the starting point. We must understand how humble the early Greeks felt when they confronted arguments like this. It was like a divine revelation. |
| 1512 | Zeno is wrong that one grain of millet makes a sound; why should one grain achieve what the whole bushel does? [Aristotle on Zeno of Elea] |
| Full Idea: Zeno is wrong in arguing that the tiniest fragment of millet makes a sound; there is no reason why the fragment should be able to move in any amount of time the air which the whole bushel moved as it fell. | |
| From: comment on Zeno (Elea) (fragments/reports [c.450 BCE], A29) by Aristotle - Physics 250a16 |
| 1508 | Zeno's arrow paradox depends on the assumption that time is composed of nows [Aristotle on Zeno of Elea] |
| Full Idea: Zeno's third argument claims that a moving arrow is still. Here the conclusion depends on assuming that time is composed of nows; if this assumption is not granted, the argument fails. | |
| From: comment on Zeno (Elea) (fragments/reports [c.450 BCE], A27?) by Aristotle - Physics 239b5 |
| 15530 | A logically determinate name names the same thing in every possible world [Lewis] |
| Full Idea: A logically determinate name is one which names the same thing in every possible world. | |
| From: David Lewis (How to Define Theoretical Terms [1970], III) | |
| A reaction: This appears to be rigid designation, before Kripke introduced the new word. |
| 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 |
| 15531 | The Ramsey sentence of a theory says that it has at least one realisation [Lewis] |
| Full Idea: The Ramsey sentence of a theory says that it has at least one realisation. | |
| From: David Lewis (How to Define Theoretical Terms [1970], V) |
| 15528 | A Ramsey sentence just asserts that a theory can be realised, without saying by what [Lewis] |
| Full Idea: If we specify a theory with all of its terms, and then replace all of those terms with variables, we can then say that some n-tuples of entities can satisfy this formula. This Ramsey sentence then says the theory is realised, without specifying by what. | |
| From: David Lewis (How to Define Theoretical Terms [1970], II) | |
| A reaction: [I have compressed Lewis, and cut out the symbolism] |
| 15526 | There is a method for defining new scientific terms just using the terms we already understand [Lewis] |
| Full Idea: I contend that there is a general method for defining newly introduced terms in a scientific theory, one which uses only the old terms we understood beforehand. | |
| From: David Lewis (How to Define Theoretical Terms [1970], Intro) | |
| A reaction: Lewis is game is to provide bridge laws for a reductive account of nature, without having to introduce something entirely new to achieve it. The idea of bridge laws in scientific theory is less in favour these days. |
| 15529 | It is better to have one realisation of a theory than many - but it may not always be possible [Lewis] |
| Full Idea: A uniquely realised theory is, other things being equal, certainly more satisfactory than a multiply realised theory. We should insist on unique realisation as a standard of correctness unless it is a standard too high to be met. | |
| From: David Lewis (How to Define Theoretical Terms [1970], III) | |
| A reaction: The point is that rewriting a theory as Ramsey sentences just says there is at least one realisation, and so it doesn't meet the highest standards for scientific theories. The influence of set-theoretic model theory is obvious in this approach. |
| 454 | If there are many things they must have a finite number, but there must be endless things between them [Zeno of Elea] |
| Full Idea: It things are many, they can't be more or less than they are, so they must be finite, but also there must be endless things between each thing, so they must be infinite. | |
| From: Zeno (Elea) (fragments/reports [c.450 BCE], B3), quoted by Simplicius - On Aristotle's 'Physics' 140.29 |
| 455 | That which moves, moves neither in the place in which it is, nor in that in which it is not [Zeno of Elea] |
| Full Idea: That which moves, moves neither in the place in which it is, nor in that in which it is not. | |
| From: Zeno (Elea) (fragments/reports [c.450 BCE], B4), quoted by (who?) - where? |
| 1511 | If everything is in a place, what is the place in? Place doesn't exist [Zeno of Elea, by Simplicius] |
| Full Idea: If there is a place it will be in something, because everything that exists is in something. But what is in something is in a place. Therefore the place will be in a place, and so on ad infinitum. Therefore, there is no such thing as place. | |
| From: report of Zeno (Elea) (fragments/reports [c.450 BCE], B3) by Simplicius - On Aristotle's 'Physics' 9.562.3 |