Locke often writes that our knowledge is the perception of the agreement or disagreement of ideas. For example, he refers to “our Knowledge consisting in the perception of the Agreement, or Disagreement of any two Ideas” in the second chapter of the Essay's book on knowledge. Similarly, at the beginning of this book he characterizes knowledge as “the perception of the connexion and agreement, or disagreement and repugnancy of any of our Ideas”. Since commentators remark on this formula so frequently, (...) one would expect that major questions about its interpretation would have been settled long ago. But not so. Controversy still prevails about Locke's intent, and especially about his assumption that the knowledge of the existence of real things counts as an instance of the perception of the agreement or disagreement of ideas.Scholars have put forward two sorts of problems about the attempted assimilation of knowledge of real existence to Locke's formula. (shrink)