Ostinato–Variations (Chaconne & Passacaglia) Theory Things   William Wieland
The terms chaconne and passacaglia are often interchanged. The following definitions allude to the Bach pieces listed first among the examples. Many pieces satisfy both definitions.
Chaconne — variations over a repeated harmonic progression (similar in concept to the 12-bar Blues)
Passacaglia — variations over a repeated bass line called the ground bass or ground (sometimes the ostinato is not in the bass) 
| III   | VII   | i | V     |
| III | VII | i   V | i |