there cannot be an A-difference without a B-difference - Slogan supervenience

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        A set of properties A supervenes upon another set B just in case no two things can differ 
        with respect to A-properties without also differing with respect to their B-properties. In 
        slogan form, “there cannot be an A-difference without a B-difference”.
      
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<p>

      
        As we shall see, this slogan can be cashed out in many different ways. But to illustrate 
        the basic idea, imagine that there is a perfect forger. Her copies of paintings not only 
        fool the art dealers, but are in fact exact duplicates of the originals down to the 
        precise placement of every molecule of pigment—indeed, down to every microphysical detail. 
        Suppose that she produces such a copy of El Greco's A View of Toledo. It is of course 
        different from the original in various respects—it is a forgery, it was not painted by El 
        Greco, it is worth quite a bit less at Sotheby's, and so forth. But the forgery is also 
        exactly like the original in other respects. It is the same shape, size, and weight. The 
        surface of the canvas contains the same arrangements of colors and shapes—a blue rectangle 
        here, a green swirl there. Indeed, it looks just the same, at least to a single viewer 
        under identical lighting conditions and so forth. Perhaps it is even just as beautiful as 
        the original, though that is more controversial.
      
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<p>

      
        he properties that the forgery is guaranteed to share with the original are those that 
        supervene upon its microphysical properties. Two paintings that are microphysically just 
        alike are guaranteed to be just alike in the arrangement of colors and shapes on their 
        canvases. That is, you cannot change the arrangement of colors and shapes on a painting's 
        canvas without changing its microphysical properties. This is just to say that the 
        arrangement of colors and shapes supervenes on its microphysical properties.
      
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<p>

      
        Supervenience is a central notion in analytic philosophy. It has been invoked in almost 
        every corner of the field. For example, it has been claimed that aesthetic, moral, and 
        mental properties supervene upon physical properties. It has also been claimed that modal 
        truths supervene on non-modal ones, and that general truths supervene on particular 
        truths. Further, supervenience has been used to distinguish various kinds of internalism 
        and externalism, and to test claims of reducibility and conceptual analysis.
      
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