<P> The modern system divides instruments into wind, strings and percussion . It is of Greek origin (in the Hellenistic period, prominent proponents being Nicomachus and Porphyry). The scheme was later expanded by Martin Agricola, who distinguished plucked string instruments, such as guitars, from bowed string instruments, such as violins . Classical musicians today do not always maintain this division (although plucked strings are grouped separately from bowed strings in sheet music), but distinguish between wind instruments with a reed (woodwinds) and those where the air is set in motion directly by the lips (brass instruments). </P> <P> Many instruments do not fit very neatly into this scheme . The serpent, for example, ought to be classified as a brass instrument, as a column of air is set in motion by the lips . However, it looks more like a woodwind instrument, and is closer to one in many ways, having finger - holes to control pitch, rather than valves . </P> <P> Keyboard instruments do not fit easily into this scheme . For example, the piano has strings, but they are struck by hammers, so it is not clear whether it should be classified as a string instrument or a percussion instrument . For this reason, keyboard instruments are often regarded as inhabiting a category of their own, including all instruments played by a keyboard, whether they have struck strings (like the piano), plucked strings (like the harpsichord) or no strings at all (like the celesta). </P> <P> It might be said that with these extra categories, the classical system of instrument classification focuses less on the fundamental way in which instruments produce sound, and more on the technique required to play them . </P>

Why can a piano be considered both a string and a percussion instrument