The connection between music and poetry has a long and indisputable tradition. There are many poets (such as Simon Armitage) eventually dedicating themselves to music, as well as there are numerous examples of musicians (such as Jim Morrison) publishing poetry at some point in their careers. Furthermore there are innumerable poems about music and its impact on us.
However, many literary critics seem to have problems with calling song lyrics poetry and Armitage himself does make a clear distinction, too: “If writing poems is like building up a papier-mache or matchstick model, layer by careful layer, piece by precarious piece, then the process of lyric writing, for me anyway, is more like whittling a piece of wood, stripping and slicing away until something clear and smooth comes into view.” In terms of the creative process, Armitage seems to experience lyric writing as something “rougher” than poetry writing.
In terms of the final product, he claims (as already mentioned in Cinzia’s post below) that “poems have their own music”. And in fact they do. Poetry is music without instruments. It has its own rhythm and melody. A song is always already an interpretation of the written word. It’s comparable to drama and the respective production of a play. Music can definitely make poetry more accessible, though, and Armitage, as a poet of the download generation, does a great job in connecting the two forms of art and thus maybe spark people’s interest in poetry in general.
Finally, I would like to quote a musician/poet who simply puts the subject of debate as follows: "Anything I can sing, I call a song. Anything I can't sing, I call a poem." May Bob Dylan live long and prosper.