 The link to poetry is clear, he tells us, given that poetry is perfected by being set to music. Besides this there are formal similarities: poetry is formed by concatenating letters from a finite alphabet, and music is formed by concatenating sounds from a finite palette. Al-Fārābī grants that in the case of music the palette is dictated by nature, whereas the letters of a national alphabet are adopted by convention in that nation ([Music] 120f). But he notes that in some cultures the music accompanying a poem is counted as a part of the poem, and that this can be justified by the fact that sometimes the poetic metre is sustained by the music rather than the words ([Poetry]  91.15–17).[24]