 Semantic externalists take these sorts of judgments about Twin Earth to militate against a traditional account of meaning—for they suggest that your understanding does not fully determine the nature of the reference. But according to Jackson, the only conclusion that is warranted is that the meaning of your term is more complex than the tradition suggests: your verdicts about possible worlds considered as actual reflect your naïve reference-fixing criterion, and your verdicts about possible worlds considered as counterfactual reflect the theoretical criterion you would accept after you learned all the relevant empirical facts about your actual environment. These two types of criterion can be modeled in possible world semantics as intensions: an A-intension (for ‘Actual’) is a function from worlds considered as actual to extensions, while a C-intension (for ‘Counterfactual’) is a function from worlds considered as counterfactual to extensions (Jackson 1998a, ch.2). The diagonal of our matrix corresponds to the A-intension you associate with ‘water’; and the first horizontal row corresponds to the C-intension of your term ‘water’ (assuming that \(\langle\)Earth, \(a, t\rangle\) represents your real-world environment).