I 105
Necessity/essential/Bigelow/Pargetter: For example, suppose you have to travel within 24h from Melbourne to London. There are different necessities, e.g. to reach a telephone or others, which can be psychological, causal, etc.
Possibility: is also ambiguous. For example, today it is physically impossible to get from Melbourne to London in 10 minutes, but perhaps not always.
I 106
Necessary/possible/Bigelow/Pargetter: we can alternatively interpret them as "always" and "sometimes".
I 224
Natural Laws/Relative Necessity/Bigelow/Pargetter: Assuming we now label a set of A of sentences as natural laws, we also denote a set of C of possible worlds where these laws are true.
Nomically necessary: then we can say that each sentence is nomically necessary iff it is true in all possible worlds of C.
Nomic necessity/Bigelow/Pargetter: is thus explained in terms of entailment by laws.
>
Entailment.
Natural Laws/Bigelow/Pargetter: Question: How do we pick out the set A of the sentences that are considered to be natural laws? That depends of course on the way the world is.
>
Natural laws.
What is considered a natural law can be different from world to world. It can only be contingently true in one world, or false in another.
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Possible Worlds, >
Possible Worlds/Bigelow.
For example, there are worlds in which Aristotle's law (see above) applies.
Then there is a set to every world w
A
w of sentences that are laws in w. That determines a set of
C
w, of world whose events coincide with the laws in w.
I 225
Nomically necessary: is then when sentence p, iff it is true in all worlds in C
w - in all worlds that are compatible with the laws in w.
>
Entailment.
Nomic necessity: Natural laws.
I 227
Natural necessity/Lewis/Bigelow/Pargetter: should be explained in terms of laws and not vice versa.
I 238
Natural necessity/Bigelow/Pargetter: is not definable by law. It is what makes laws laws!
