Full Idea
I hold that characteristic theoretical identifications like 'heat is the motion of molecules', are not contingent truths but necessary truths, and I don't just mean physically necessary, but necessary in the highest degree.
Gist of Idea
Identities like 'heat is molecule motion' are necessary (in the highest degree), not contingent
Source
Saul A. Kripke (Naming and Necessity lectures [1970], Lecture 2)
Book Reference
Kripke,Saul: 'Naming and Necessity' [Blackwell 1980], p.99
A Reaction
This helps to keep epistemology and ontology separate. The contingency was in the epistemology. That the identity is 'physically necessary' seems obvious; that it is necessary 'in the highest degrees' implies an essentialist view of nature.