Like the scale harmonization or rule of the octave, many of the most commonly used chord progressions have their origins in the 17th and 18th centuries. Recent research has provided insight into 'schemata', or a set of frequently used progressions (also used within the partimento tradition). Each of these schemata has a specific function, such as closing a musical sentence, creating an ascending or descending movement, etc. In his book Music in the Galant Style, Robert Gjerdingen discusses 18th-century schemata in detail. For more interesting examples and research, visit www.essaysonmusic.com by Ewald Demeyere.