What is music in opera? In Monteverdi's Orfeo, his first opera, music is arguably the protagonist, whether La Musica in the prologue, whose ritornello guides Orfeo to and from the Underworld, or embodied in the legendary singer himself, who uses his musical prowess to charm the guardians of Hell. In Il ritorno d'Ulisse, however, there is no such protagonist, no single embodiment of musical power. In the largest sense, of course, and in contrast to straight drama – the plays of Euripides, Shakespeare or Calderon may have some music in them but are essentially spoken – all of Il ritorno d'Ulisse, all of most operas, is music. But in Monteverdi's sense (and in the librettist Badoaro's), that music is divided into ‘speech’ and ‘song’ – or, speech-like and musical utterances.

A number of scholars have drawn attention to the importance of Parisian popular theatre for an understanding of Verdian dramaturgy, especially in the operas leading up to Rigoletto, Il trovatore and La traviata. According to Giovanni Morelli, in Paris, Verdi frequented the popular theatre not for the sake of participating in the active milieu of Romantic cultural thought (Milanese circles had adequately fulfilled that need), but in order to mingle with a typical metropolitan theatre audience in the venues dedicated to the dissemination of a watered-down, middlebrow form of Romanticism.

It is sometimes remarked that Wagner's prose works would not be of much interest if their author had not also turned his creative energies in a very different direction. What is not often observed, however, is the influence this truism has exerted on critical approaches to the theoretical writings. A tacit consensus dictates that these texts be seen as marginalia, ancillary documents whose value lies in the light they shed on immeasurably more important achievements. We have inherited the prose works in the form of useful gnomic tags: Gesamtkunstwerk, ‘endless melody’, ‘deeds of music made visible’ – fragments of text extracted from their context and pressed into service as authoritative pronouncements about the operas. More extensive analysis has usually been concerned with the relation between the written theories and the works they are understood to describe. There is a powerful hierarchy implicidy at work: text (theory) is subservient to music (practice); the former is at best an interpretative tool.

One of the central events of the film Moonstruck (1987) takes place in a performance of La bohéme at the Metropolitan Opera. Loretta (Cher) is puzzled by what seems to be Mimì's unexpected death, which takes her by surprise, even though the explanation by her friend Ronny (Nicholas Cage) reveals that she suspects its cause. Most of us will smile indulgently at a first-time opera-goer's ingenuous conflation of character (‘coughing her brains out’) and voice (‘keep singing’). But we might pause for a moment on a more intriguing twist in Loretta's surprise at Mimì's death – the fact that our antibiotic age has largely forgotten the devastating epidemic formerly known as phthisis or consumption.

In the age of AIDS, few would be surprised to find sexuality connected to suffering and disease; in the age of syphilis – from its arrival in Europe in 1492 to today, when it is on the rise once again – the connection is equally strong, though many of us have forgotten this. The brief respite offered by the discovery of a cure for syphilis (through the use of penicillin) in the 1940s ended with the appearance of AIDS. Over the last five hundred years, the Christian reading of syphilis as the scourge of God directed against the sexually sinful has merged with societal sexual anxieties about the effects of syphilis on the general social fabric and, in the nineteenth and twentieth centuries, on the family in particular. The perhaps surprising focus of this discussion (by a literary theorist and a physician) of suffering and social decline in the context of sexually transmitted disease is Richard Wagner's last music drama, Parsifal, finally completed in 1882 and called a Bühnenweihfestspiel (a stage consecration festival play) for his Bayreuth theatre.