Ideas from 'Could There Be Unicorns?' by Michael Dummett [1983], by Theme Structure
[found in 'The Seas of Language' by Dummett,Michael [OUP 1993,0198236212]].
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4. Formal Logic / D. Modal Logic ML / 1. Modal Logic
16951

It was realised that possible worlds covered all modal logics, if they had a structure

4. Formal Logic / D. Modal Logic ML / 3. Modal Logic Systems / a. Systems of modal logic
16952

If something is only possible relative to another possibility, the possibility relation is not transitive

16953

Relative possibility one way may be impossible coming back, so it isn't symmetrical

4. Formal Logic / D. Modal Logic ML / 3. Modal Logic Systems / d. System T
16960

If possibilitiy is relative, that might make accessibility nontransitive, and T the correct system

4. Formal Logic / D. Modal Logic ML / 3. Modal Logic Systems / g. System S4
16958

In S4 the actual world has a special place

9. Objects / D. Essence of Objects / 10. Essence as Species
16955

Kripke says internal structure fixes species; I say it is genetic affinity and a common descent

10. Modality / E. Possible worlds / 1. Possible Worlds / a. Possible worlds
16957

Possible worlds aren't how the world might be, but how a world might be, given some possibility

10. Modality / E. Possible worlds / 1. Possible Worlds / c. Possible worlds realism
16959

If possible worlds have no structure (S5) they are equal, and it is hard to deny them reality

23. Ethics / C. Virtue Theory / 1. Virtue Theory / d. Virtue theory critique
16956

To explain generosity in a person, you must understand a generous action

26. Natural Theory / B. Concepts of Nature / 6. Natural Kinds / g. Critique of kinds
16954

Generalised talk of 'natural kinds' is unfortunate, as they vary too much
