"This," Glyn Maxwell writes on the first page of his new book, "is a book for anyone." This is, to say the least, a dubious claim. Given that the market for poetry in Britain is vanishingly small, the market for books about poetry is ... well, suffice to say that Oberon Books are to be congratulated on putting this out, because it really is a tremendously good book, and should be read by anyone who writes poetry and anyone who's interested in how and why poetry is written.

Or anyone who's interested in what poetry is. What is it about this form with its short, jagged-edged lines, its patterning of words and sounds? What makes it different from chopped-up prose? On this, as on much else, Maxwell is brisk and forthright: if you're going to write poetry, "line-break is all you've got, and if you don't master line-break  the border between poetry and prose  then you don't know there is a border. And there is a border. (A prose poem is prose done by a poet.)"

Within a few pages more, he has dealt comprehensively, too, with the seemingly eternal debate about the relationship between poetry and song. Recently on the Guardian website John Sutherland was discussing the morality of rap music (surely a category mistake, akin to debating the efficiency of bananas, but that's another matter). Not surprisingly, the piece generated plenty of comments from readers; perhaps more surprisingly, the thing that many of them picked up on was the line in which the doyen of Eng lit, and presumed defender of the canon, wrote: "Those words ... by Shakur, Ice Cube, and Snoop Dogg can legitimately take their place in what we regard as poetry, not music."

Your response to the question of whether the work of 50 Cent, say, or Jay-Z counts as poetry will depend not only on your opinion of the work per se, but on what you think poetry is. It's clear from the Sutherland comments that for some, the word "poetic" means something like "lyrical" or "inspiring" or "thoughtful". Or, less approvingly, perhaps "flowery", "high-minded" or "overblown" could be workable synonyms. This point of view sees the epithet "poetic" as a kind of value judgment: these lyrics are so good they qualify as poetry  as if that was the nicest compliment that could be bestowed on them.

There's plenty of poetry that isn't "poetic" in this sense. You could argue that the whole direction of 20th-century poetry was towards weeding out poetry that was "poetic". Indeed, it's probably a pretty good definition of bad poetry. And if you see "poetic" only as a positive value judgment, the idea of bad poetry must be a contradiction in terms. But believe me, there really is such a thing as bad poetry.

What Maxwell calls poetry, good or bad, is different from song precisely because it carries its own music within it. Where song lyrics are written to function within a musical frame, poetry is framed by silence; it's always working against the void. "Poets work with two materials, one's black, one's white," Maxwell writes. "You want to hear the whiteness eating? Write out the lyrics of a song you love  If you strip the music off it, it dies in the whiteness, can't breathe there." It isn't a question of whether a Bob Dylan song, or something by Grandmaster Flash is as good as a Keats ode or something by Auden. In the end Maxwell is refreshingly clear on the issue: "Bob Dylan and John Keats are at different work. It would be nice never to be asked about this again."

It should be clear by now, despite the somewhat po-faced title, that what Maxwell has written isn't some dry technical textbook, or manual of creative writing school exercises. The chapter titles themselves  "White", "Black", "Form", "Pulse", "Chime", "Space", "Time"  read like something Ezra Pound might have written at his most gnomic, but they announce that this is something out of the ordinary. There are things here that you could take as exercises, if you want to (he recommends interesting things to do with nine blank sheets of paper, for instance), but it's not essential. And there's a diverting narrative line running through it, too, involving three creative writing students who wind up at the wedding feast in "The Rime of the Ancient Mariner".

The point is that there's nothing high-minded or grandiose about this  it's fun. Poetry "has been unnecessary for almost all of creation", Maxwell admits. "Strictly speaking, it still is." This is a book written by someone who has devoted a great deal of thought to what it is he does when he works out a poem, and it's informed by his practice as both a writer and a teacher. It's a masterclass in close reading and close writing  that is, in paying proper attention to the weight of words and their various shades of meanings, to their musical value and how one word affects its neighbour. "All I believe, and therefore all I teach  which is why I don't need a book any longer than this, though I could talk a very long night on the placing of 'the'  is that the form and tone and pitch of any poem should coherently express the presence of a human creature." That's not a bad summation of what we value about good poetry.

I've struggled, on occasions, to feel at home with some of Maxwell's own verse. But this is the best book about poetry I've ever read; certainly the only one that's made me laugh out loud. Maxwell's students are lucky to have him, and so are the rest of us.