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1. INTRODUCTION
locke defines knowledge at the beginning of Book IV of the Essay concerning Human Understanding as "the perception of the connexion and agreement, or disagreement and repugnancy of any of our Ideas" (E IV.i.2).1 So defined, knowledge varies along two dimensions. On the one hand, there are four "sorts" of knowledge: of identity or diversity; relation; co-existence or necessary connection; and real existence. On the other hand, there are three "degrees" of knowledge: intuitive knowledge, which consists in the "immediate" perception of agreement or disagreement between ideas (E IV.ii.1); demonstrative knowledge, which consists in the perception of agreement or disagreement by way of intermediate (or intervening) ideas; and sensitive knowledge, which is less certain than either of the other degrees, and is knowledge of "the particular existence of finite Beings without us" (E IV.ii.14).
This paper considers the well-known tension between Locke's definition of knowledge and his claim that we can know of the existence of things without the mind by sensation. According to the general definition of knowledge, knowledge consists in perceiving agreements or disagreements of ideas.2 As the marginal summary for E IV.i.2 makes clear, this is to be understood specifically as the claim that knowledge consists in perceiving agreements between ideas, and not the agreement of our ideas with anything else; hence, Locke introduces the definition of knowledge by explaining that
Since the Mind, in all its Thoughts and Reasonings, hath no other immediate Object but its own Ideas, which it alone does or can contemplate, it is evident, that our Knowledge is only conversant about them. (E IV.i.1)3
However, sensitive knowledge appears to depend less on agreements between ideas than on agreements between our ideas and the mind-independent particulars that they are ideas of. This raises two questions. First, is Locke's claim that we can have knowledge of the existence of mind-independent particulars inconsistent with his general definition of knowledge, as commentators since Stillingfleet have often suggested?4 Second, does Locke's general epistemological framework lead inevitably to skepticism, as commentators since Stillingfleet have also often suggested? If all that is ever directly present to the mind is our ideas, then how can we know of the existence of anything independent of those ideas? As Hume puts it,
Let us chace...