Hyperbole is not usually the first word one associates with "The Lake Isle of Innisfree," but if we understand hyperbole to mean not only exaggeration, but "claims [that are] not meant to be taken literally," as Google defines it, we can begin develop a context for understanding the poem through this lens.
The poem does use hyperbole in the sense of "claims not meant to be taken literally." Yeats was inspired to write this poem...
Hyperbole is not usually the first word one associates with "The Lake Isle of Innisfree," but if we understand hyperbole to mean not only exaggeration, but "claims [that are] not meant to be taken literally," as Google defines it, we can begin develop a context for understanding the poem through this lens.
The poem does use hyperbole in the sense of "claims not meant to be taken literally." Yeats was inspired to write this poem while living in London by memories of childhood visits to the Isle of Innisfree in County Sligo, Ireland. What emerged in the poem was an idealized vision of a place of peace and harmony, a pastoral setting far from the rush and bustle of urban life. In it, Yeats dreams of building a small cabin of "clay and wattles," where he will cultivate "nine bean rows" and a beehive and enjoy being alone in the "bee-loud glade."
The simplicity of the life he envisions is exaggerated for effect. He would probably, in reality, want more than a cottage, nine bean rows and a bee-hive, but the very starkness of these images comes to symbolize the simplicity he seeks. Likewise, he probably wouldn't want to always be alone, but the image of the poet in solitude with his cottage, beans and beehive conveys a deep sense of peace.
In the second stanza, Yeats offers the heightened image of a bright night sky: "the midnight's all aglimmer" and a parallel heightened mellowness in the "purple glow" of noon, purple being a color we more often associate with dusk than midday. Again, rather than literal, these images imply a gentle mellowness heightened for effect: the night is not too dark, nor the day too bright.
In the third and final stanza, Yeats writes that "always night and day/I hear lake water lapping." Again, we are not meant to take literally that Yeats "always" hears the water. It means instead that he has internalized the feeling of peace that his images of the isle bring and will try to carry this peace with him in his soul.
The starkness of the images functions on a level that is not literal but which uses exaggerated simplicity meant to inspire the reader to strip away what is unnecessary and, like the poet, find life's core essentials.