How can I recognise a work from the 20th Century?

It can sometimes be difficult to distinguish between works of the Romantic period and those of the 20th Century. This is largely owing to the themes of intense emotion that characterise works of both periods. However, a crucial focus of 20th Century work is on the expression of feelings as intensely as possible - hence the name of the Expressionist movement. This is in contrast to works of the Romantic period, which largely focussed on expressing emotion through life-like, realistic musical painting. Music of the 20th Century pioneered atonality - music that is not in any key. Their experimental nature often called for larger orchestras (including piccolos, bass clarinets, and contrabassoons) and drastic changes in instrumentation, resulting in many contrasts in timbre. Furthermore, unusual effects might be employed such as in Peripetie (Schoenberg), where cymbals are occasionally played with both a mallet and a cello bow.