The use of written characters ([Greek: sêmeia]) to represent the sounds of music appears to date from a comparatively early period in Greece. In the time of Aristoxenus the art of writing down a melody ([Greek: parasêmantikê]) had come to be considered by some persons identical with the science of music ([Greek: harmonikê]),--an error which Aristoxenus is at some pains to refute. It is true that the authorities from whom we derive our knowledge of the Greek notation are post-classical. But the characters themselves, as we shall presently see, furnish sufficient evidence of their antiquity. [Footnote 1: Ptol. _Harm._ ii. 6. After drawing a distinction between difference of key as affecting the whole of a melody or piece of music and as a means of change in the course of it--the distinction, in short, between transposition and modulation proper--he says of the latter: [Greek: hautê de hôsper ekpiptein autên] (sc. [Greek: tên aisthêsin]) [Greek: poiei tou synêthous kai prosdokômenou melous, hotan epi pleon men syneirêtai to akolouthon, metabainê de pê pros heteron eidos, êtoi kata to genos ê kata tên tasin.] That is to say, the sense of change is produced by a change of genus or of pitch. A change of _species_ is not suggested. So Dionys. Hal. _De Comp. Verb._ c. 19 [Greek: hoi de ge dithyrambopoioi kai tous tropous] (keys) [Greek: meteballon, Dôrikous te kai Phrygious kai Lydious en tô autô asmati poiountes; kai tas melôdias exêllatton, tote men enarmonious poiountes, k.t.l.]]