A poster of some renown with a one-track mind has asked a question, but refuses to put it out in the open. So to speak. The question is: "What about pornography in classical music?" Well, yes: what about it?
We do know that some of the music to Attic Greek comedies accompanied suitably scatalogical and pornographic material, because the lyrics (by people like Aristophanes) have survived. It would be nice to say this was a theme that continued up to the present time, given humanity's nature. But we can't do that, because many cultures had different, and stricter, rules than our own concerning what sort of written content could be set to music or placed on stage.
We first begin seeing sexual content filtering back into Western European classical music in the 14th century, thanks to several Florentine carnival songs that have survived. These were not the equivalent of our modern carnivals, but more like the Mardi Gras: nominally religious festivals that temporarily exploded the fabric of society. Imagine, if you will, an intricate, sweetly sung four-part madrigal about the artichoke, which goes, in part, as follows:
First, ladies, you must hoe all around,
take the leaves in hand and then bind it,
cover it, and sow it absolutely straight:
there are some who plant it lying face down.
The artichoke should be in size
a span or a little more, for nature
cannot digest anything so big and hard,
even though we always like the big mouthfuls...
Alas, although we have the music and the text, there's nothing that reproduces the gestures that we're certain accompanied this dulcet piece.
The late Renaissance English were also fond of this kind of thing, and there are many popular songs and classical transcriptions that survive of similar material. In fact, there's a fair amount of raunchy, euphemistic material along these lines, and some that actually gets a lot more hardcore over the next couple of centuries, before Protestantism set in and outlawed the stuff. Huge bonfires of plays, books, and musical compositions were burnt in cities throughout Central and Western Europe by militant Protestants who felt it was an afront to Christianity.
You have to jump forward to Mozart, then, to encounter our next stop in classical smut. The guy was nothing like the figure portrayed in Amadeus, but he did enjoy dirty jokes. One of his amusements was to create canons on the first tone--several different melodies in the same key, which overlapped naturally and without causing disonance. He would set each melody to an innocent lyric which, combined with the others, would at some point in the number, give rise to a line that was completely lewd. Mozart used to meet with several friends, all of whom were among the shining lights in classical performance in Vienna, high a meal, drink heartily, and then try these out. Fortunately, they have survived, to the embarassment of many generations of music appreciation teachers, everywhere.
The late 19th and all of the 20th century witnessed a level of tolerance for the open disclosure of sexually related materials in Western urban culture that hasn't been seen since the Renaissance. There have been attempts to reimpose controls--the 1950s in the United States, British Prime Minister John Major's "campaign for decency," de Gaulle's attempt to reinstitute censorship on a national level in France. Thus far, these have been passing moments, and classical composers, like everybody else, have taken advantage of this greater openness. Texts set to classical music have become increasingly frank, even obscene by many standards. When text wasn't used, it was still possible to get across a lot in music--such as Paul Dukas' sensual ballet, La Peri. (Dukas also possessed one of the largest collections of French porn in existence. It's now in the National Library in Paris. Think about this fact the next time you listen to The Sorcerer's Apprentice.)
If you want more information, you'll just have to read up on the stuff. Try Grove's Dictionary of Music and Musicians, for a start. The volumes are big enough to fit around a Playboy or Playgirl issue, too.