Certain portions of the fugue in _A_ major, further, produce the effect of concerted music, conceived for different tone-colors, rather than that of a polyphony of like sounds, especially where broken chords occur in the counterpoint. At other times, when the pedal is silent, a trio-sonata is suggested. This does not surprise us; Bach was still preoccupied with the forms of Italian chamber music. We have noted the transformation which his preludes underwent under this influence, they now being constructed upon distinct subjects; and we have seen in the Toccata in _C_ how Bach sought to write a work in three movements, each one of a different character and tempo, in imitation of the concertos and sonatas. Here and there again, as in this instance, we find attempts at three-part writing clearly defined;[108] not merely because the pedal remains silent, but by reason of a plainly indicated design. [Footnote 108: For example, in the fugue in _G_ minor (P. iv, 7).] Bach aligned these endeavors in definite order, classified their essentials, and embodied them in the sonatas, or rather trios, for two manuals and pedal.[109] [Footnote 109: P. i, 1. B.-G. xv.] Play these trios upon the organ, and you will divert them from their original destination. Bach composed them for the clavecin with two manuals and pedal, between the years 1722 and 1727,[110] for the purpose, Forkel tells us, of instructing his eldest son, Wilhelm Friedemann, in organ-playing, through their use in home practice. [Footnote 110: The first part of the sonata in _D_ minor undoubtedly dates from the year 1722; the _adagio_ and _vivace_ of the sonata in _E_ minor are transcribed from the cantata _Die Himmel erzählen_ (1723), B.-G. xviii. The last movement of this sonata was originally intended to serve as an interlude between the prelude and the fugue in _G_ major (P. ii, 2. B.-G. xv, p. 169. The theme of the fugue is, in major, that of the first chorus in the cantata _Ich hatte viel Bekümmerniss_, performed in 1714), composed, according to the water-mark of the autograph, in 1724 or 1725.] The structure of these sonatas is analogous to that of the six violin sonatas of Bach with clavecin accompaniment; they still lack the definite form of the modern sonata;[111] they are more, as has been said, "lyric pieces." [Footnote 111: See S. Bagge: _Die geschichtliche Entwickelung der Sonate_.] If Bach wrote these trios to accustom his son to the technical difficulties of the organ, perchance considering them only a set of studies, and for himself an interesting occupation by which he might profit, his motives in writing the Fantasie and Fugue in _G_ minor[112] were, apparently, very different, and may be definitely connected with the journey which he made to Hamburg in 1720. This is an hypothesis which is sustained by a whole chain of circumstances. [Footnote 112: P. ii, 4. B.-G. xv, p. 177.]