Before concluding Book 2, Locke makes some final distinctions between our ideas. They can be clear or obscure, distinct or confused, adequate or inadequate, real or fantastical, and true or false. Locke does not say anything very novel in any of these chapters, drawing heavily on the distinctions already made by Rene Descartes. A clear idea is fresh and exact in the mind, while an obscure one is fuzzy. A distinct idea is one we can distinguish well from all other ideas, and a confused one is the opposite. An adequate idea perfectly represents what it purports to represent, while an inadequate one imperfectly or only partially represents what it purports to represent.

In the context of adequate and inadequate ideas, Locke makes some comments regarding substances (his prime example of inadequate ideas) that prove very useful in relation to discussions in Book 3. A real idea is one that has a foundation in nature, while a fantastical one does not. "True" and "false" are not adjectives that can apply to ideas strictly speaking, except insofar as we assume either that our idea is exactly like someone else's idea, that our idea conforms to the real existence of things, or that our idea refers to the real constitution of things (there will be much more on this in Book 3).

Locke concludes Book 2 with a reflection on why people can easily recognize irrationality in others but not in themselves. He claims that idiosyncratic bonds are forged by chance between certain of our ideas that do not belong together by nature. These strong bonds mislead our reasoning. We are not, however, prone to the strong bonds among ideas that lead others astray, and so we easily see their reasoning as faulty.


Other philosophers before had made all of these distinctions before, in almost exactly the same language. The most interesting distinctions, those between clear and obscure ideas and distinct and confused one, are lifted directly from Descartes' Principles of Philosophy. The other distinctions are hardly novel or thought provoking.