Criteria for classical music?

Your answer is not entirely correct. Indeed, many works for piano and guitar, but .. what about the symphonies of Beethoven, Sibelius etc.? What about the opera Puccini, Verdi? There is no piano or guitar at all! These criteria are very complicated issue. Not to mention the term "classic" is very ambiguous. Therefore I always call it MUSIC LITERATURE, rather than classical music. The criteria was simple: music is music written literature. If it is full of jazz improvisation: The main theme is always there, but every performance sounds different. If folk music was taught orally, from generation to generation. If the music literature (such as Bach, Beethoven, Sibelius, to modern music such as Aaron Copland, Shostakovich, Benjamin Britten ... and my own) that the composer wrote down everything she wants. With musical notes, with the signal, with written information, etc.. So it could be reproduced with a more practical, and therefore this music (which is of high quality, of course), can "stand against the times," because of his manuscripts there.