excerpt from A Defence of Poetry

For language is arbitrarily produced by the Imagination and has relation to thoughts alone; but all other materials, instruments and conditions of art, have relations among each other, which limit and interpose between conception and expression...We have thus circumscribed the meaning of the word Poetry within the limits of that art which is the most familiar and the most perfect expression of the faculty itself.

 

 
NOTES: Poetic language expresses the Imagination best because speech is directly related to our thoughts. It is the problem of mediation; words are our best mode of conveying our thoughts. The Imagination creates thoughts, and language is "a more direct representation of our the actions and passions of our internal being." Shelley holds poetry as the highest form of art, superior to music, painting, and sculpture.