John Locke is the greatest English philosopher. <EM>An Essay Concerning Human Understanding</EM>, one of the most influential books in the history of thought, is his greatest work. In this study the historical meaning and philosophical significance of Locke''s <EM>Essay</EM> are investigated more comprehensively than ever before.<BR><EM>Locke</EM> was originally published in two volumes, <EM>Epistemology</EM> and <EM>Ontology</EM>. This paperback edition has within its covers the full text of both volumes.