Ideas from 'How to Define Theoretical Terms' by David Lewis [1970], by Theme Structure

[found in 'Philosophical Papers Vol.1' by Lewis,David [OUP 1983,0-19-503204-7]].

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2. Reason / D. Definition / 2. Aims of Definition
Defining terms either enables elimination, or shows that they don't require elimination
10. Modality / E. Possible worlds / 3. Transworld Objects / b. Rigid designation
A logically determinate name names the same thing in every possible world
14. Science / B. Scientific Theories / 8. Ramsey Sentences
There is a method for defining new scientific terms just using the terms we already understand
A Ramsey sentence just asserts that a theory can be realised, without saying by what
The Ramsey sentence of a theory says that it has at least one realisation
It is better to have one realisation of a theory than many - but it may not always be possible