 Generalized 2D semantics seeks to vindicate a traditional internalist conception of meaning: it posits an extra aspect of meaning for all expressions (the intension corresponding to the diagonal of a 2D matrix) that is fully determined by a subject’s internal states, and which in turn determines objective truth-conditions for their sentences. By enriching compositional semantics in this way, G2D promises a straightforward explanation of a variety of epistemic properties of sentences: e.g., why a necessary sentence like ‘Hesperus is Phosphorus’ is not apriori knowable, what the subject learns by accepting the sentence, or how the subject uses the sentence in reasoning.