there is a definite second subject in, by the way, the minor key of the dominant, and it is divided from the first by two bars in common time (a descending scale and a shake on a semibreve).  And then again, in No. 12 of the “Libro de XII.  Sonatas Modernas para Clavicordio,” the second subject is divided from the first by two bars of common time (the piece is in Scarlatti’s favourite measure, three-eight), an ascending scale and a shake.  There are clear examples of a second subject, besides E. Bach, in Eberlin, Fleischer, J.C.  Bach, and J.C.F.  Bach.  Yet even in Haydn’s sonatas one cannot always speak of a second subject.  The further history of the development of the contents of the second half of the first section shows, as it were, a struggle between two ideals.  One was kinship, i.e. the endeavour to present the secondary matter in strong relationship to the opening one (the opening notes or bars of a real second subject were, indeed, frequently the same, allowance being made, of course, for difference of key); the other was contrast, i.e. the endeavour to obtain variety.  Haydn was more affected by the first; Mozart by the second.  In Beethoven the two are happily combined.  It is important to notice the closing bars of many first sections of the period of which we are speaking.  For instance, in E. Bach, the first movement of the sonata in each of the Collections of 1781 and 1783 has a concluding theme (as in the sonata of Scarlatti, and frequently evolved from the opening theme).  Though in the complementary key, it cannot count as “the second subject.”  It appears after the complementary key has been ushered in by one cadence, and after having apparently run its course, it has been wound up by another.  Then, again, the portion between the cadences just mentioned is at times filled with a true theme, so that the concluding one, like the cave of Abraham’s field of Machpelah, is in reality an appendency. Sometimes there are several:  the enlargement of the exposition section by Beethoven, and still more modern composers, so that it contains sometimes three, and even more themes, is practically an exposition section on Scarlatti lines, only on a larger scale:  the figure has become a phrase, mere connecting passages have acquired organic meaning.  The second section of Scarlatti’s movement in binary form contained a few bars of development and modulation.  Then a return was made to the opening key of the piece, but never to the opening theme; and in that key a portion more or less great, more or less varied, according to circumstances, was repeated.  That return to the opening theme is, as we have already said, the landmark which divides binary from sonata form.