Is music a language? And if so what requirements should a language satisfy?

There is no uncontroversial definition of a language. However, a requirement that is often cited is that there should be rules on how different elements of a language are composed together (syntax). Another requirement is that the elements of a language should have representational content (semantics). Music arguably passes the first requirement: notes cannot be strung together in any way one likes to make music. But it appears to fail the second requirement: it is not obvious that individual musical notes represent anything at all. One might argue that sometimes there are phrases in music that do represent: for example, different instrumental lines in Prokofiev's Peter and the Wolf represent the activities of different animals. But these tend to be rather isolated cases of representation; they are not as widespread and systematic as one would expect from a language (e.g. flutes in music do not always represent birds, or indeed anything at all). Even if music is not a language in the above sense...