Full Idea
Critics say there are no irreducible a posteriori truths. They can be factored into a part that is necessary, but knowable a priori through conceptual analysis, and a part knowable only a posteriori, but contingent. 2-D semantics makes this precise.
Gist of Idea
Critics say there are just an a priori necessary part, and an a posteriori contingent part
Source
Robert C. Stalnaker (Conceptual truth and metaphysical necessity [2003], 1)
Book Reference
Stalnaker,Robert C.: 'Ways a World Might Be' [OUP 2003], p.202
A Reaction
[Critics are Sidelle, Jackson and Chalmers] Interesting. If gold is necessarily atomic number 79, or it wouldn't be gold, that sounds like an analytic truth about gold. Discovering the 79 wasn't a discovery of a necessity. Stalnaker rejects this idea.