 But assuming (4), why would EXT render (1) apriori? Granted, many externalists find it apriori plausible that besides interacting with water, Oscar could acquire the water concept from other community members. That suggests that if Oscar has acquired the concept, (4) must be true. However, some externalists conjecture that there are other conditions under which the water concept can be acquired. Even if Oscar is socially isolated and lives in a waterless environment, he can conceivably arrive at the concept by hypothesizing the H2O molecule (Burge 1982). If this cannot be ruled out apriori, then EXT does not secure the apriority of (1)—even if (4) is assumed.