 This claim about linguistic meaning is then extended to the content of mental representations for natural kinds like water, and for non-natural kinds like sofas (where the latter are defined by social convention) (McGinn 1977, Stich 1978, Burge 1979; 1982; 1986). Consider that when Oscar says “sofas are delightful,” he expresses a thought that references sofas. But suppose that Twin Oscar’s community defines a “sofa” slightly differently, so that broad, overstuffed armchairs count as “sofas.” Consequently, when Twin Oscar asserts “sofas are delightful,” he differs from Oscar in expressing a thought that refers to (among other things) broad, overstuffed armchairs. But again, if content determines reference, the difference in reference demonstrates a difference in intension or content, in spite of identical internal  states.[9]  Thus we arrive at EXT.