From the FT's review of Potters's tenor voice book

by Luigi Speranza for "Gli Operai" jlsperanza@aol.com

Until the early 17th century the tenor usually wrote his own music to showcase his vocal talent. For the next three centuries, as opera established itself, the composer remained at the service of the performer. Just as the 17th-century tenor would use the written line as a basis for florid ornamentation, so the 19th-century tenor would interpolate high notes to show off his virtuosity and increase his popularity.

That came to an end in the late 19th and early 20th centuries. Composers regained control partly through the influence of Wagner, whose emphasis on stamina and dramatic expression left no room for empty display. But also partly through the conductor Arturo Toscanini, whose reign at La Scala, Milan, and the Metropolitan Opera, New York, enforced the doctrine of come scritto – singing the music “as written”, not as a vehicle for wilful improvisation. The downside was the loss of “something unrecoverable – the tenor as creative artist linked to a tradition dating back hundreds of years”.

The only blip in the tenor’s inexorable rise was in the 18th century, when the castrato took precedence. However improving social conditions soon put paid to the mutilations required to produce such a voice. By the late 19th century the tenor had taken on his modern form, with the additional resonance, higher notes and greater volume demanded by larger theatres and fuller orchestration – but at the cost of a flexible lower voice.