Formally, poetry is recognizable by its greater dependence on at least one more parameter, the line, than appears in prose composition. This changes its appearance on the page; and it seems clear that people take their cue from this changed appearance, reading poetry aloud in a very different voice from their habitual voice, possibly because, as Ben Jonson said, poetry “speaketh somewhat above a mortal mouth.” If, as a test of this description, people are shown poems printed as prose, it most often turns out that they will read the result as prose simply because it looks that way; which is to say that they are no longer guided in their reading by the balance and shift of the line in relation to the breath as well as the syntax.
