Full Idea
Bear in mind the contrast between the a priori but perhaps contingent properties carried with a natural kind term, given by the way its reference was fixed, and the analytic (and hence necessary) properties a term may carry, given by its meaning.
Gist of Idea
The properties that fix reference are contingent, the properties involving meaning are necessary
Source
Saul A. Kripke (Naming and Necessity lectures [1970], Lecture 3)
Book Reference
Kripke,Saul: 'Naming and Necessity' [Blackwell 1980], p.135
A Reaction
The second half of this is the 'new essentialism'. Complex. We need to distinguish 'reference' from 'definition'. The 'analytic properties' seem to be the definition, but we sometimes change our definitions (e.g. of units of time).