In this paper I argue that Locke takes sensitive knowledge (i.e. knowledge from sensation) to be genuine knowledge that material objects exist. Samuel Rickless has recently argued that, for Locke, sensitive knowledge is merely an “assurance”, or a highly probable judgment that falls short of certainty. In reply, I show that Locke sometimes uses “assurance” to describe certain knowledge, and so the use of the term “assurance” to describe sensitive knowledge does not entail that it is less than certain. Further, (...) I show that sensitive knowledge includes the perception of a relation between ideas, and thus it satisfies Locke’s definition of knowledge. He also repeatedly claims that sensitive knowledge is certain. So, despite recent challenges to this interpretation raised in the secondary literature, Locke really does take sensitive knowledge to be certain knowledge. (shrink)