Locke characterizes sensitive knowledge as knowledge of the existence of external objects present to the senses, and in terms of an ‘assurance’ that falls short of the certainty of intuition and demonstration. But it is unclear how this fits with his general definition of knowledge, as the perception of the agreement or disagreement of ideas, and it is unclear how that assurance can amount to knowledge, rather than amounting to mere probability (which he contrasts with knowledge). Some contend that Locke (...) does not regard sensitive knowledge as genuine knowledge, but only honourifically calls it knowledge. In contrast, I argue that Locke holds that sensitive knowledge is knowledge, though he takes the conditions for it to be very different from the conditions for intuitive and demonstrative knowledge. It is not the assurance alone which Locke thinks qualifies sensitive knowledge as such: it is also the fact that the assurance arises from the actual employment of the senses upon external objects, and the fact that the senses do not generally deceive us, which he thinks qualifies sensitive knowledge as genuine knowledge. That there is a (tacit) form of externalism in Locke's account of sensitive knowledge is the main thesis of this paper. (shrink)