 Following Frege (1892), Chalmers is interested in capturing a notion of meaning that is finer-grained than reference. Frege pointed out that sentences containing co-referential expressions like ‘Hesperus’ and ‘Phosphorus’ can differ in cognitive significance: someone who is competent with these two names may not realize they are co-referential and may therefore use them differently in making and justifying claims. Frege took sameness of cognitive significance to be the mark of sameness of meaning. According to a 2D rationalist, sameness of cognitive significance can in most cases be elucidated in terms of apriori equivalence: two expressions are associated with the same meaning iff one can know that they pick out the very same things on the basis of apriori reflection alone (Chalmers  2002b).[14]  This constitutive link between meaning and apriority constitutes the first side of the “golden triangle”.