For Bob Hanna? Donald Davidson against one conceptual scheme (an Analysis-like paper)

Donald Davidson argues against the claim that others have an alternative conceptual scheme, even that they could have such a thing: a radically different system of concepts for interpreting the data of sensation. But he strangely goes further: he also denies that mankind has one conceptual scheme, because "How can we intelligibly speak of one, if there cannot be two?" Sir P.F. Strawson asserts that this surely goes too far in his opposition to talk of conceptual schemes. But which premise or inference Davidson relies on is mistaken? Hans Johann-Glock has objected on the grounds that we can intelligibly speak of one thing without being able to intelligibly speak of two, if we can distinguish this thing from some other thing, which may not be a thing of the same type, in this case may not be another conceptual scheme. I argue that Glock's objection fails and I present a different objection to Davidson: that speaking of one scheme is a reasonable shorthand for "There are certain concepts that all (language-using) humans share." One may believe this or merely discuss this under the heading of "There is only one conceptual scheme."