The central theme of John Locke's Of the Conduct of the Understanding is human error. The Conduct was conceived as an additional chapter to An Essay concerning Understanding, but it was never finished and published posthumously in 1706 as a separate work. Modern authors have regarded the Conduct as an educational treatise. Indeed, the analysis in this work of the nature and causes of error and the ways to prevent and remedy error gives rise to numerous educational reflections. However, the aim of the present article is to show that these views should be understood within the specific epistemological context of a two-stage analysis of ideas, the first stage consisting of individual ideas that should all be clear and distinct, and the second stage consisting of reasonings based on combinations of these ideas.