 Epistemic 2D semantics differs in important respects from traditional accounts of meaning. Semantic theories normally describe general semantic rules governing expression types, whereas epistemic 2D semantics is based on a single individual’s current understanding of a token expression. Kaplan and Jackson, for instance, use the 2D framework to characterize the implicit conventions governing syntactically individuated expressions like ‘I’ or ‘water’ in our linguistic community. In contrast, Chalmers uses the 2D framework to characterize your potentially idiosyncratic understanding of a particular use of an expression on a given occasion—e.g., the way you understood Al Gore’s fifth use of ‘water’ during a speech on climate change. Moreover, on this account 2D semantic values depend on the upshot of ideal rational reflection about apriori coherence relations. Just what is involved in ideal rational reflection is an open question. But it’s plausible that it may depend on substantive constructive theorizing about the empirical scenario in question and on various non-obvious and idiosyncratic aspects of the subject’s initial cognitive state. In that case, identifying the precise epistemic 1-intension associated with your understanding of ‘water’ will be a highly non-trivial matter, and it may be far from obvious when your understanding of the term shifts so that two tokens no longer share the same epistemic 1-intension. This is why, in contrast with 2D empiricists like Jackson, a rationalist like Chalmers denies that epistemic 1-intensions reflect the subject’s “implicit knowledge” of a reference-fixing criterion (e.g., Chalmers 2002a, 185; 2006b, §5).