We may say that a poem in the first place should offer us new perceptions, not only of the exterior universe, but of human experience as well; it should add, in other words, to what we have already seen. This is the elementary function for the reader. The corresponding function for the poet is a sharpening and training of his sensibilities; the very exigencies of the medium as he employs it in the act of perception should force him to the discovery of values which he never would have found without the convening of all the conditions of that particular act, conditions one or more of which will be the necessity of solving some particular difficulty such as the location of a rhyme or the perfection of a cadence with disturbance to the remainder of the poem.