I've been following the list as a lurker for some time and am glad
some of the people I remember as very knowledgeably continue to post
here occasionally.  I want to leap back in with a question that has
been tormenting me for quite a while, for which I haven't been able
to find an answer anywhere else.

When one looks at the description on the back of a symphonic CD,
one is likely to find each movement characterized by the tempos to
be employed-allegro, moderato, presto, etc.  Yet in an opera, sections
tend to be designated by their form-aria, cavatina, duetto, etc.  I've
concluded that this is because most orchestral movements are composed
of some version of sonata form.  I have noticed that sometimes other
forms are identified (and, in these cases the tempo is omitted) as with
menuetto and trio, rondo, theme and variations, etc.

Am I on the right track?  Is this a convention with a rationale or is
it simply tradition?

Zeke