If Domenico Scarlatti's contemporaries heard the B-theme of his sonata K.208 (L.238) as less than outrageously unstable with respect to its key, it is hard to see why the key instability of Wagner's Tristan (composed about a century later) should have been greeted with much more than 'big fucking deal'.
Here is Scarlatti's proto-Wagnerian harmonic pretzel in a performance by the Korean pianist Soo-Yeon Ham recorded live at the 2009 Cleveland International Piano Competition.
