The contemporary division into old and new music might be a bit misleading. Or to be frank: it is very misleading! After all, at some point in history early music was the latest music, thoroughly avant-garde, often incomprehensible not only for audiences but also for musicians. When faced with new ideas, the latter would sometimes consider them bizarre and simply ignored them. Claudio Monteverdi experienced this himself when introducing new sound effects in his Dramatic Il combattimento di Tancredi e Clorinda. The pizzicato had been more or less acceptable, so was the four-voice system for the strings group (replacing the prevailing five voices). But when it came to the tremolos enhancing the dramatic tension, the Venetian violinists simply exchanged the lengthy series of repeated, quick notes into one, long note of the same height. It goes without saying that this ruined the desired effect, vital for the work that initiated the stile concitato (“agitated style”) in music. In 1638, 14 years after the premiere, Monteverdi was preparing his composition for print, he did not fail to mention his combattimento di compositor e li violinisti and explain in detail why he took the trouble of writing down the same note sixteen times, instead of making it into one long lie.
This shows that Monteverdi was a  truly avant-garde composer and only time made him a respectable classic – this is at least what we usually think of him until we begin to play his music. It then comes alive again with a richness of ideas so great that not all are taken up by successive generations of artists. Four centuries passed and the music is still fresh and surprising.
György Ligeti is a classic of our time. Passing away ten years ago, the composer was obviously thoroughly avant-garde, but his techniques became generally adopted over time. An example is micropolyphony: voices weaved so thick, imitations so intertwined, impossible to be perceived in detail. Sometimes even the artist divided his ensemble into two smaller ones, each tuned according to a different tuning fork, like in the Ramifications for 12 string instruments.
Ligeti composed only one “real” opera (Le Grand Macabre) which he called an anti-opera anyway. Later on, he merged three soprano arias into one para-theatrical scene:  Mysteries of the Macabre. The opera was a turning point for Ligeti, who henceforth began intensively drawing from earlier music. Rarely was his inspiration a straightforward quotation or pastiche (Ligeti’s preferred source of inspiration was Monteverdi) – he aimed for a more creative use of old ideas and forms – for instance, by using the pasacaglia and chaconne forms in two harpsichord pieces. His Monteverdi inspirations can also be traced down to the works of his radically avant-garde period. Aventures and Nouvelle Aventures cannot be pigeonholed in terms of genre. However,  in formal terms, these para-theatrical pieces for three soloists are quite close to Il combattimento.