The concept of "epistemology" as a distinct field of inquiry predates the introduction of the term into the lexicon of philosophy. John Locke, for instance, described his efforts in "Essay Concerning Human Understanding" (1689) as an inquiry "into the original, certainty, and extent of human knowledge, together with the grounds and degrees of belief, opinion, and assent". According to Brett Warren, the character "Epistemon" in King James VI of Scotland's "Daemonologie" (1591) "was meant to be a personification of would later come to be known as 'epistemology': the investigation into the differences of a justified belief versus its opinion."