he impulse to give an already successful
composition a larger or more permanent form, in such cases as the
transformations undergone by the movements of the birthday cantata, _Was
mir behagt ist nur die muntre Jagd_, during their distribution among the
church cantatas, _Also hat Gott die Welt geliebt_ and _Man singet mit
Freuden vom Sieg_. The fine bass aria, "Ein Fuerst ist seines Landes Pan,"
was obviously ill-proportioned, with its breakneck return to the tonic and
its perfunctory close; and Bach's chief concern in adapting it for its
place as the aria, "Du bist geboren mir zu Gute," in _Also hat Gott_, was
to remedy this defect. On the other hand, the use of the delightful
ritornello for violoncello from the little aria, "Weil die wollenreichen
Heerden," in the birthday cantata, and the restoration of the rejected long
instrumental _fugato_ that was to follow, were obviously brought about by
the conception of the entirely new material for the voice in the famous
aria, "Mein glaeubiges Herze." And when the last chorus of _Was mir behagt_
became the first chorus of _Man singet mit Freuden_, it was expanded to the
proportions necessary for a triumphant opening (as distinguished from a
cheerful finale) by the adroit insertion of new material between every
joint in the design. This material, being new, could not produce the effect
of diffuseness that would result from the expansion of the old material
already complete in its simplest form, and thus this instance does not
imply criticism.

A highly interesting example of pure self-criticism is the _Passion
according to St John_, which was twice revised, and each time reduced to a
smaller scale by the omission of some of its finest numbers. The final
result was a work of perfect proportions, and of the rejected numbers one
(a magnificent aria with chorale) remained unused, two were replaced by
finer substitutes, others took shape as one of the most complete and
remarkable of the church cantatas, _Du wahrer Gott_, while the greatest of
the figured chorales was transferred to the _Passion according to St
Matthew_, of which it now crowns the first part.

3. Such instances of self-criticism might be paralleled in the works of
other composers; but there is no parallel in music to Bach's power of
reproducing already perfect works in different media. Here Bach reveals to
us identities in difference which we should otherwise never have suspected.
Of course it is possible to arrang