 Roughly, the idea is that ‘Hesperus = Phosphorus’ is aposteriori because we associate distinct reference-fixing criteria with the two names: e.g., being the brightest star visible in the evening and the brightest star visible the morning. According to the 2D rationalist, these reference-fixing criteria are (i) an aspect of meaning, (ii) which can be known apriori via conceptual analysis, and (iii) which suffices to fix the applicability conditions for every possible world considered as one’s actual environment. If the 2D framework can be used to isolate such an aspect of meaning for all expressions, we will have vindicated the rationalist’s “golden triangle” connecting meaning, apriority and possibility.