"Metamorphoses" is the plural of "metamorphosis," and my question is, did German composer Paul Hindemith name his best known orchestral work Symphonic Metamorphosis or Symphonic Metamorphoses? I'd thought it was "Metamorphoses," but a recent article in the NYTimes used the singular. Google turns up both titles in published reference works.
The answer is easy, but the source of the confusion is interesting. As reported by the official Hindemith website, the work is called Symphonic Metamorphosis of Themes by C. M. von Weber--the singular, as in the Times. Hindemith wrote the work in 1943 to be premiered by the New York Philharmonic, and the original title is in English.
When put into German, however, the metamorphoses multiplied. The German title is Symphonische Metamorphosen nach Themen von C. M. v. Weber, with the German plural Metamorphosen instead of the singular Metamorphose. (No one seems to use Symphonische Metamorphose, singular, as the German title.) The French follow suit with Métamorphoses symphoniques d'après des thèmes de C. M. von Weber, unmistakeably plural. If someone assumed (wrongly) that the German title was original, back-translating into English would give the erroneous title *Symphonic Metamorphoses.
Notice too how Hindemith's unassuming "of" becomes "nach" (= "after") in the German title. Still, you can see why whoever created the German title would have wanted to adjust the original: a direct translation from the English would give in German something like Symphonische Metamorphose von Themen von C. M. von Weber. That's one von too many for anyone's taste.
[German composer Sigfrid Karg-Elert wrote a Symphonic Metamorphosis for organ, completed in 1930 but not published, and rediscovered only in 1984. Did Hindemith know Karg-Elert's title? Or did he come up with Symph. Met. himself? Did they both get it from somewhere else? I'd like to know.]