Jonathan Ellis wrote:

>And when is somebody going to mention the most sublime chaconne ever
>written: "When I am laid to earth," from "Dido and Aeneas"?

I have refrained from putting in my two bits on this thread but the urge
overwhelms me now.  In my experiences with music, both listening and
performing, a chaconne is a piece of music based on a recurring harmonic
pattern whereas a Passacaglia uses a recurring melody which does NOT need
to be the bass line.  Some of the Baroque lute (transcribed for guitar)
pieces I have played were Passacaglias and the main melody which so
commonly occurs in the bass also can appear in the upper registers with
nothing related happening in the bass.

Now as for as the Purcell piece you mention, which I feel is one of the
most beautiful pieces written in history, this is a piece of music upon a
ground.  Purcell was the truest master of this form.  Pieces on a ground
consist of a bass line which NEVER changes unless, as Purcell himself has
done, the exact same bass melody is just played in another key.  Purcell
LOVED the ground bass and even went as far as to say it is a terribly easy
form to write in.

As far as I have learned through my own studies:
Chaconne: Common harmonic sequence throughout.
Passacaglia: common melody throughout; usually in the bass but not always.
Ground: Unwavering bass line, never changes; music changes above it.

Hope my two bits have been as helpful as all the other bits!

Wes Crone