This book presents a history of nineteenth century metaphysics in Britain, providing close textual readings of the key contributions to First Philosophy made by the key philosophers of the period (such as Hamilton, Mansel, Spencer, Mill, and Bradley) as well as some lesser known figures (such as Bain, Clifford, Shadworth Hodgson, Ferrier, and John Grote). The story focuses on the elaboration of, and differing reactions to, the concept of the unknowable or unconditioned, first developed by Sir William Hamilton in the 1829. The idea of an ultimate but unknowable way that things really are in themselves may be seen as supplying a narrative arc that runs right through the metaphysical systems of the period in question as, relative to this concept, these thought schemes may be divided into three broad groups which were roughly consecutive in their emergence but also overlapping as they continued to develop. In the first instance there were the doctrines of the agnostics who further progressed Hamilton’s basic idea that fundamental reality lies for the great part beyond our cognitive reach, but these philosophies were followed, immediately by those of the empiricists and, in the last third of the century by those of the idealists, both of whom—albeit in profoundly different ways—reacted against the epistemic pessimism of the agnostics. By presenting, interpreting, criticizing and connecting together their various contrasting ideas this book explains how these three traditions developed and interacted with one another to comprise the history of metaphysics in Victorian Britain.