On the Plurality of Worlds, by David Lewis#

"This book is a defence of modal realism: the thesis that our world is but one of a plurality of worlds, and that the individuals that inhabit our world are only a few out of all the inhabitants of all the worlds."

If I swallow the philosophic modality pill, then I find myself in much agreement with Lewis in various debates. However, I find the whole subject to be mis-guided. I think of possibilities as branching from free-will decisions and (potentially) non-deterministic physical laws. Anything that did not actually happen is only possible if these branchings could have given it---i.e., the physical laws are fixed, as is free will. And, these possibilities are not linguistic or abstract constructions, but mathematical configurations of choices.#

In my mind, many things that these philosophers find possible, I find not to be, such as talking donkeys. Based on LDS theology, i.e., my belief in co-eternal intelligences (separate from spirits, bodies, and souls); you could say I believe in haecceities and other essential properties.#

Some parts of Lewis' argument I found very intriguing: non-world beliefs (p. 28); doublethink (p. 35); how imagination and possibility are not the same (p. 90); "Whatever the truth may be, it isn't up to us" (p. 114); his argument that modal realism does not promote scepticism, it merely gives the old argument new form (p. 116), along with an interesting "proof" about primes (p. 119); and egocentric properties, again (p. 125).#