By considering all of Thomas's prose work in its wide variety of genres (nature writing, literary criticism, fiction, autobiography) and by drawing, for the first time, on the whole range of his reviewing, this study transforms understanding of his development. The continuity of his critical perspective emerges; his Celtic loyalties, their nature and their depth, are revealed; both the complexity and the conviction of his politics are brought to light, alongside his receptive alertness to innovative writing and his own originality and daring as a writer. The view of his achievement generated by his interwar reception (itself the outcome of societal mourning and griefwork) is challenged; so is the critical consensus regarding the quality of his prose and the reasons behind its changing styles across Thomas's career. From all of this, it becomes clear, moreover, how powerfully Thomas's work speaks in the contemporary moment of environmental and climate breakdown. Thomas's prose seeks constantly to articulate a relationship of absolute interdependence between human beings and the natural world. His writing is so exploratory and original because Thomas seeks to address the problematic reality that interdependence--this truth of humanity's place in natural world--is perceptible to Western eyes only as mystery.