Full Idea
The three sources of necessity - the identity of things, the natural order, and the normative order - have their own peculiar forms of necessity. The three main areas of human enquiry - metaphysics, science and ethics - each has its own necessity.
Gist of Idea
Each area of enquiry, and its source, has its own distinctive type of necessity
Source
Kit Fine (The Varieties of Necessity [2002], 6)
Book Reference
Fine,Kit: 'Modality and Tense' [OUP 2005], p.260
A Reaction
I would treat necessity in ethics with caution, if it is not reducible to natural or metaphysical necessity. Fine's proposal is interesting, but I did not find it convincing, especially in its view that metaphysical necessity doesn't intrude into nature.