Research through practice into the actual process of composing, such as William James on automatic writing and thought processes, or Sigmund Freud on creative writing and the unconscious, is rare, and needs extension and updating. This study builds a new theoretical framework for critical and practical work on imaginative composition by investigation of Edward Thomas's composing processes and complementary analysis of the processes of writing my own poetry collection. Thomas's emphasis on fragmentation of thought, hesitancy and silence in the content and form of his poetry, positioning him on the borders of Modernism, reflects essential aspects of his composing processes, as documented in his notes, letters, prose and poetry. The creating and revisiting of my own works-in-progress and final collection, in the light of the study of Thomas and in dialogue with readers, reveals further insights into poetic composition. Chapter One examines the point at which poems emerge and the influence of external writing conditions. Chapters Two and Three look at absence in the composing process in ellipses, aporia, gaps and unfinishedness, and in the art of submission as it is used in composing. Chapter Four investigates distraction, non-logical connections and physical and temporal disturbances in composing. Chapter Five shows the importance when composing of sustaining a flexible and exact attention to immediate perceptions and thoughts. The thesis concludes with an original poetry collection resulting from the documentation of my composing processes during the research period. These poems reflect and refract many points made in previous chapters, offering practical evidence of them. The principles of poetic composition established in this thesis are also more generally applicable to the composing of poetry. Similarities observed in composition processes in other art forms and in the writing of this thesis indicate that these principles also apply to other creative and academic disciplines, providing areas for further research.