First, I did want to point out that my claim that "Mozart was never able to" didn't mean that I thought he wasn't able to compose fugues, rather I thought he wasn't able to compose fugues WELL--definite emphasis on "well".
Second, what I mean by "composing a fugue well" is to be able compose a piece or movement whereby three or more, usually four, voices are heard in a contrapuntal, not harmonic, manner for an EXTENDED PERIOD OF TIME (i.e., maintaining this for many measures).
I looked closely at some of the examples people brought up like the last movements of both the Jupiter Symphony and his String Quartet No. 14 and nowhere do I see 4 voices simultaneously acting contrapuntally for more than just a handful of bars. Mozart would often write a given voice contrapuntally, but would often quickly revert that voice to a harmonic function. If you look at measures 91 to 106 in the last mvt of Quartet No. 14, that writing is a joke if you say he can write fugally. The second violin, viola, and cello are all mainly serving a harmonic function; they're just playing chords. One part that might look truly fugal would be in measures 112 to 117, but that's just one small part and not extended, as in the great fugues of Bach and Beethoven. Measures 61 to 90 kind of look truly fugal, but he really only has 3 voices going contrapuntally here at any given time, not 4. Look at measures 63 until 68 where the cello is playing an extended rest, for example.
Yes, Mozart wrote fugues. Did he write truly sophisticated, truly "fugal" fugues? I still think not.
Second, what I mean by "composing a fugue well" is to be able compose a piece or movement whereby three or more, usually four, voices are heard in a contrapuntal, not harmonic, manner for an EXTENDED PERIOD OF TIME (i.e., maintaining this for many measures).
I looked closely at some of the examples people brought up like the last movements of both the Jupiter Symphony and his String Quartet No. 14 and nowhere do I see 4 voices simultaneously acting contrapuntally for more than just a handful of bars. Mozart would often write a given voice contrapuntally, but would often quickly revert that voice to a harmonic function. If you look at measures 91 to 106 in the last mvt of Quartet No. 14, that writing is a joke if you say he can write fugally. The second violin, viola, and cello are all mainly serving a harmonic function; they're just playing chords. One part that might look truly fugal would be in measures 112 to 117, but that's just one small part and not extended, as in the great fugues of Bach and Beethoven. Measures 61 to 90 kind of look truly fugal, but he really only has 3 voices going contrapuntally here at any given time, not 4. Look at measures 63 until 68 where the cello is playing an extended rest, for example.
Yes, Mozart wrote fugues. Did he write truly sophisticated, truly "fugal" fugues? I still think not.