How much?

[12tone.]

A very beginner question...

In the earlier music era of Mozart (and older) in parts for harpsichord (in symphonies) and other instruments how much of what we hear in recordings / live performances is from what has been written down and how much is improvised?

I know there are those cadenzas where the performer was free to improvise or use what the composer put down, but I'm talking about non-cadenza material.

How much of what we hear is from the pen as it were?  We could go through the eras.

How much of what we hear was actually from the composer's hand:

- Ren Period:

- Baroque

- Classical

- Romantic

- 20th Century
B

[12tone.]

No one knows?

[Montpellier]

Regarding Mozart, I'd guess that almost everything except cadenzas was written.  Editors do get their fingers in these works occasionally but substantially they must be as written. 

I don't know enough about Mozart to say that he wrote for continuo/figured bass (may be possible for recitative passages) in which case, just the harmony was indicated rather than the actual melody notes.  This was a common practice in baroque times.   I'd venture that the intent of composition from the classical era onwards is to play as written unless directed otherwise - cadences, "ad libs" etc, but these are exceptions. 

The Renaissance isn't at all clear.  Lithurgical music seems to be sung/played as written, subject to certain conventions to give some kind of sense to cadences and the like. 

20th Century.   Most music in the earlier part of the century is played as written but from the 1950s on, a lot depends on supplemental instructions given by composers.  With composers like Cage, one understands that a recording or performance is just one view, a snapshot if you like, of that work and its next performance might sound like a different piece.
 

[m_gigena]

Regarding Mozart, I'd guess that almost everything except cadenzas was written.  Editors do get their fingers in these works occasionally but substantially they must be as written. 

Didn't he leave the solo part of the 26th concerto incomplete, as he improvised during the performances?

[Grazioso]

Keyboardist Robert Levin has an interesting article on improvisation in Mozart's music here:

http://www.aam.co.uk/index.htm (Go to "More" --> "Features" and scroll/search down for "Improvising Mozart".)