 This simple rationalist picture of meaning and modality, however, was undermined by externalist thought experiments. Kripke’s (1980) observation that certain necessary truths, like ‘Hesperus = Phosphorus’, are only knowable aposteriori threatens both the idea that linguistic competence affords apriori access to the truth- and applicability-conditions of one’s words and the idea that necessary truths are always apriori knowable. The guiding idea behind 2D rationalism is that a rationalist can accommodate Kripke’s examples by moving to a 2D semantic framework. In particular, the 2D framework can be used to isolate an aspect of meaning that satisfies the “golden triangle” of constitutive relations among meaning, apriority and modality.