Ignaz Pleyel - Symphony in C minor, B.121

[ironflange]

This piece should be described as being in C major, or at least C major/minor, as the slow intro is the only part set in the minor mode.

[jossuk]

Actually, the source document doesn't mention a key; the title would be (merely) Sinfonie Periodique.
It would seem that Identifying works by key may have evolved into an obligatory format, regardless of the composer's intentions.