An Enquiry Concerning Human Understanding was written by Scottish naturalist philosopher David Hume and published in 1748. The work is a significant reworking of the early parts of Hume’s 1737 Treatise on Human Nature, which had received a reception that Hume found underwhelming. In An Enquiry Concerning Human Understanding, Hume builds upon the empirical philosophy of John Locke and George Berkeley, and attacks the metaphysical rationalism of René Descartes and others.
An Enquiry Concerning Human Understanding is decidedly a book about epistemology and not about metaphysics. That is, Hume is concerned about what and how we know, and not at all about what is actually the case.