So what was Beethoven thinking about then? Possibly simply about the musical materials and the fabric one can weave with them. But it is often thought that what he was implying by this comment was that he was writing, not for the players, or even for the current audiences, but for the future--posterity, in other words.
Carl Dahlhaus in his book on musical aesthetics says this:
There is a widespread opinion that ranks the tenacity with which a musical work resists perishing and survives in performance or at least sticks in memory as the most decisive of all criteria that determine the work's importance. This opinion has become a commonplace, which no one doubts, least of all a public that feels pleased and assured in an awareness that it is the last court of appeal. ... To suppose that a work surviving for decades or even centuries owes this survival only to itself, its structure, and its expressive value, is a modern superstition. [Dahlhaus, Esthetics of Music, p. 97]He goes on to mention the indestructibility of some pieces that have, as he says, "devolved" into anonymity such as La Paloma:
This was written by the Spanish composer Sebastián Yradier in 1863 before dying in obscurity. As a guitarist, the Spanish Romance, composer unknown, comes immediately to my mind:
Neither of these pieces is particularly beloved by critics, but they have little effect on this kind of musical immortality. As Dahlhaus comments,
Any criticism in merely esthetic or technical terms, no matter how well-founded, remains ineffective in the face of the demands of the music business, in which there is a turbid mixture of practical compulsion and laziness. [op. cit. p. 98]Dahlhaus mentions other factors in the survival of musical works such as institutional or functional support as in the case of Gregorian chant (supported by the Catholic Church) and national anthems (that have a political function).
Many of the most popular and indestructible pieces of classical music came from the pen of Beethoven such as "Für Elise":
Certainly not a great piece, but one that sticks in the mind. The Moonlight Sonata is a great piece and one that has achieved indestructible immortality (or at least for a few decades or a few hundred years perhaps):
Two other of the most famous and popular classical pieces are also by Beethoven: the Symphony No. 5 and Symphony No. 9. The main theme from the last movement of the latter has even achieved national anthem status as it is the anthem of the European Union:
How do composers think about this sort of thing? Perhaps Beethoven was thinking of posterity, or perhaps he was thinking, at least in the case of the symphonies, that they would become successful and popular almost immediately, as they did. It is likely the case that composers in the 20th century thought mostly about posterity as they were often faced with uncomprehending audiences that, in many cases, remain uncomprehending to this very day.
What does "posterity" really mean? I think that for most composers it means anything from a year, the time it might take for a work to find a venue for a premiere, to a decade--perhaps a few decades at most. Do composers really think further than that? Does any composer think, "this piece I am writing right now will not be appreciated by more than a tiny number of people for at least fifty years." If you are thinking that, then you are probably also figuring out a way to collect royalties into those distant years.
Actually, we have evidence that Stravinsky was thinking in those terms because he revised a number of his early works, like Petrouschka, for the specific purpose of regaining copyrights lost when the communists came to power in Russian. The revised version, which was now the "official" version, had a copyright dating from its revision in 1947. The original music was written in 1911.
Let's have a listen to Petroushka, one of Stravinsky's early ballets for Diaghilev and the Ballets Russes: