I don't think that Hulme found a home in either movement. His desire to develop Imagism arose from the idea that prior movements failed to accurately speak of the condition of what is. Hulme felt that the understanding of the "image" was not something that Romanticism or Classicism fully grasped. To capture "the image," outside of the realm of human interaction and sensibility is where Hulme sought to develop his ideas. For the Classicists that preceded Romantics, the mind was the filter through which the image was to be understood. For the Romantics that followed, the heart and emotional frames of reference became the tool to understand "the image." In both of these, Hulme felt that the experience of the "image" was lacking. For Hulme, the "untouched material of experience" defined the "image." Romanticism and Classicism failed in this paradigm. Both sought to appropriate the image in their own frame of reference. From a philosophical point of view, Hulme's desire to develop his theory of Imagism arose out of a fundamental dissatisfaction with both schools of thought. In this, I am not entirely certain that Hulme would fully embrace either Romanticism or Classicism.
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