 The 2D semantic frameworks proposed by Jackson and Chalmers are very similar in their broad aims and formal structure, and commentators often treat the two versions as interchangeable. However, the two frameworks are developed in the service of two quite different philosophical projects, emphasizing different aspects of the traditional approach to meaning. Jackson takes up the traditional empiricist project of explaining empirical facts about language use and communication, while Chalmers pursues a broadly rationalist project of explaining key structural interconnections between meaning, apriority, and possibility. This difference in explanatory aims leads to different interpretations of the 2D framework.