(Vienna, April 20, 1782, to his sister Marianne. Here Mozart
gives us evidence of his manner of composing; he worked out his
compositions completely in his mind and was then able, even after
considerable time had elapsed, to write them down, in which
proceeding nothing could disturb him. In the case before us while
engaged in the more or less mechanical labor of transcription he
thought out a new composition. Concerning the fugue and its
origin he continues to gossip in the same letter.)

19. "The cause of this fugue seeing the light of this world is my
dear Constanze. Baron von Swieten, to whom I go every Sunday, let
me carry home all the works of Handel and Sebastian Bach after I
had played them through for him. Constanze fell in love with the
fugues as soon as she had heard them; she doesn't want to hear
anything but fugues, especially those of Handel and Bach. Having
often heard me improvise fugues she asked me if I had never
written any down, and when I said no, she gave me a good
scolding, for not being willing to write the most beautiful
things in music, and did not cease her begging until I had
composed one for her, and so it came about. I purposely wrote the
indication 'Andante maestoso,' so that it should not be played
too rapidly;--for unless a fugue is played slowly the entrance of
the subject will not be distinctly and clearly heard and the
piece will be ineffective. As soon as I find time and opportunity
I shall write five more."

(Vienna, April 20, 1782, to his sister Marianne. Cf. No. 93.
[Mozart's remark that he carried home "all the works" of Handel
and Bach, must, of course, be read as meaning all that were in
print at the time. H.E.K.])