My music teacher claimed that no one knew the distinction between a
passacaglia/passacaille/what have you and a chaconne/ciacona/etc.  When I
made this claim on rmc I was promptly taken to task for it, as I recall,
and told that a passacaglia was in 3/4 meter and a chaconne was in 4/4
meter (iirc.) (Others say that a passacaglia has a constant repeating bass
while a chaconne has a constant repeating harmony, which is of course not
necessarily the same thing- different notes from that harmony may appear in
any given variation, given a harmonic scheme in which there is a fairly
well-defined concept by which two simultanieties (sp?) are potentially part
of the same harmony (G-B-F and G-B-D-F, say, or even G-B-D and G-B-D-F- the
presupposition of something like common tonal harmony, with its dominant
sevenths, would be necessary to the proposition that those are in some
sense the "same" harmony for the purpose of a chaconne variation set.
Anyhow, I babble.)

-Eric Schissel