The dissertation identifies two major lines of thought within the idea of 'solitude': the theme of retirement, a concern with social setting and environment, leading to retreat to the country; and the theme of isolation, a philosophical concern with individual identity and relationship with the world. It traces the development, through the eighteenth century and specifically in Coleridge and Wordsworth, from the overwhelming predominance of the retirement theme, to a concentration on the issues of isolation, springing out of but superseding those of retirement. The idea of solitude moves from a conoern with physical environment to an inspection of the processes of mind and its interaction with the world. Four eighteenth-century poets are discusaed, and the tensions that develop within their work: Thomson's reconciliation of retirement and action; Gray's concentration on the problem of serviceability in the world; Beattie's Minstrel who moves from isolation to the lessons of social experience; and Cowper's retreat which must yet generate useful employment. The dissertation turns briefly, for a comparison of differences in approach, to the works of Zimmerman and Rousseau, before focusing on the poetry of Coleridge and Wordsworth. It explores Coleridge's Conversation Poems, and the Ancient Mariner, referring also to the later prose writing and notebooks, and discusses Coleridge's concern with an individual's attempts to impose his own approach upon reality; the need to learn both individuality and acquiescence; and the search, continually renewed, for a resolving synthesis between them. Wordsworth's poetry is examined in detail, in particular his approach to the great solitary figures and to his own solitude; his probing of the balance between individual, distinct existence and absorption in the world; his realisation, ultimately, of the need for an understanding, not a resolution, of the tensions within the dilemma of self and relationship.