John Locke's complex masterpiece, An Essay of Human Understanding, was a sustained attack on the dogmatism of the day and the last great work of philosophical realism before the onset of idealism. Michael Ayers recovers its historical meaning through careful explanations of the context of debate to which it was a decisive contribution. The first volume of this comprehensive work focuses on Locke's Essay from the epistemological side The second volume turns to the concepts f Locke's ontology: substance, mode, essence, law, and identity.