Voice crossing

[8] It's not always avoided, however; Gradus ad Parnassum (1725), probably the most famous species counterpoint instruction book, includes an example using crossed voices early in the text.

An early example of medieval voice-crossing can be found in what Richard Taruskin (2009, p. 394) calls “English twinsongs.” “These songs, among the earliest polyphonic vernacular settings to survive in any language, employ a more sophisticated sort of voice-leading, through contrary motion and voice crossings.”[16] Further examples of voice crossing can be found in music of the fifteenth century, where “the voices overlap constantly.”:[17] The early seventeenth century, as in this canon by Michael Praetorius: The eighteenth century, as in Bach’s Concerto for Two Violins: And the late nineteenth century , in the finale of Tchaikovsky's 6th Symphony “which begins with a composite melody that is shattered among the whole string section (no single instrumental group plays the tune you actually hear, an amazing, pre-modernist idea)”[18] As Tom Service points out, Tchaikovsky's approach to instrumentation here was indeed prophetic.

Some nineteen years after the première of the "Pathétique" symphony, Arnold Schoenberg was exploring a similar voice crossing technique involving flute, clarinet and violin in "Ein Blasse Wascherin", a movement from his seminal melodrama Pierrot Lunaire (1912).

It leads to ambiguity, as the ear interprets the step from B to C in one voice, and is fairly consistently avoided in contrapuntal writing.

[20] Voice overlaps are common in Bach chorales, but again are discouraged or forbidden by most theory texts.

Kyrie, "Cunctipotens genitor" from Ravenna 453 f. 14r (14th century) showing one note of voice crossing
Line 3 of "Quy non fecit" from Parma bib. pal. 3597; the voices cross at the barline
Edi beo
Edi beo
Dufay , chanson "Mon chier amy"
Dufay, chanson "Mon chier amy"
Viva la Musica, canon by Michael Praetorius
Viva la musica
Bach Concerto for 2 violins in D minor, bars 26-9
Bach Concerto for 2 violins in D minor, bars 26-9
Tchaikovsky Symphony 6, finale bars 1-6
Tchaikovsky Symphony 6, finale bars 1-6
Example of two-voice overlap; if the lower voice went only to B, that would not constitute overlap.