In spite of the evident centrality of philosophical 'realism' in Collingwood's autobiographical account of his own intellectual development, his critique of 'realism' has hardly been investigated as a central theme in his philosophy. Collingwood's arguments against contemporary 'realism' and his stated move beyond 'idealism' have mostly been treated as a minor question subordinate to other questions. By contrast, I have tried in this thesis to reconstruct Collingwood's philosophy as a critical development of the realism/idealism dispute of his day, focusing on (...) his less known early published and unpublished philosophical writings. This has enabled me to clarify his unique definition of 'realism' in terms of a dualistic framework, and understand his philosophy as an attempt to overcome such dualisms in the realms of philosophy. This approach ultimately highlighted the aim of Collingwood's reform of philosophy as the better understanding of the human mind and action. By employing the 'historical' and 'internal' method of analysis, I firstly illustrated how the idea of 'dualism' became an issue in the realism/idealism dispute as it emerged in early twentieth-century British philosophy. This was followed by a biographical sketch in which I demonstrated that Collingwood's educational background was perfectly equipped to refute the 'realist' philosophy in the dispute. Historically contextualising thus, I chronologically restored the formation of his critique of 'realism' as his attempts to synthesise dualisms in logic, ontology, epistemology, and ethics during the period between Religion and Philosophy and An Essay on Philosophical Method. Finally, I argued that Collingwood's critique of 'realism' crystallised in his notion of duty, which embodied his characterisation of philosophy as both 'normative' and 'descriptive'. Throughout, I presented a systematic and sustained picture of Collingwood's early philosophy, identifying and unfolding the fertile implications of his critique of 'realism' for his principal concern with the human mind and action. (shrink)