|Necessity, philosophy: different kinds of necessity are distinguished, differing in their strength. For example, physical, logical or metaphysical necessity. See also necessity de dicto, necessity de re._____________Annotation: The above characterizations of concepts are neither definitions nor exhausting presentations of problems related to them. Instead, they are intended to give a short introduction to the contributions below. – Lexicon of Arguments. |
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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.
Necessary/possible/Bigelow/Pargetter: we can alternatively interpret them as "always" and "sometimes".
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.
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.
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. For example, there are worlds in which Aristotle's law (see above) applies.
Then there is a set to every world w
Aw of sentences that are laws in w. That determines a set of
Cw, of world whose events coincide with the laws in w.
Nomically necessary: is then when sentence p, iff it is true in all worlds in Cw - in all worlds that are compatible with the laws in w.
Nomic necessity: > Natural laws
Natural necessity/Lewis/Bigelow/Pargetter: should be explained in terms of laws and not vice versa.
Natural necessity/Bigelow/Pargetter: is not definable by law. It is what makes laws laws!_____________Explanation of symbols: Roman numerals indicate the source, arabic numerals indicate the page number. The corresponding books are indicated on the right hand side. ((s)…): Comment by the sender of the contribution.
J. Bigelow, R. Pargetter
Science and Necessity Cambridge 1990