Changes

The Aristotelian scholastic approach to knowledge saw scientific knowledge as certain knowledge of necessary truths, with conclusions deduced from premises that were self-evident. Like many others of his times, Locke did not believe that this sort of knowledge was generally possible in natural philosophy, though he continued to hold it as an ideal. He sought to replace these such stringent demands with ones more compatible with the new experimental science, such as that practiced by the Royal Society. He took knowledge to be "nothing but the perception of the connection and agreement, or disagreement and incompatibility, of any of our ideas", with our ideas derived ultimately from sensations. [[CiteRef::Locke (2015d)|p. 196]][[CiteRef::Kochiras (2014)]] Locke distinguished between two sorts of knowledge, knowledge of '''nominal essences''' which are the set of observable qualities we use to classify a thing, and knowledge of '''real essences''' which are the causal grounds of a substance's perceivable qualities. It was this latter sort of knowledge that Locke thought was, for the most part, beyond human reach.[[CiteRef::Osler (1970)]]

For Locke, the deepest sort of knowledge one might have in natural philosophy would be knowledge of the real essences of material substances and the necessary connections of these essences to qualities flowing from themwas the deepest sort of knowledge one might, in principle, have in natural philosophy. He imagined this to be knowledge of the corpuscles that make up matter and their sizes, shapes, and arrangements. Given such fundamental knowledge, we could deduce the tertiary qualities of substances; their powers to produce certain effects in other substances. Just as a locksmith knows that a particular key opens one lock but not another, we could know that opium produces sleep, and hemlock causes death and the reasons why.[[CiteRef::Locke (2015d)|p. 212]][[CiteRef::Kochiras (2014)]] But Locke supposed that such knowledge was, for the most part, beyond human faculties because corpuscles are too small to be discerned by human senses. He wrote that "But while we lack senses acute enough to discover the minute particles of bodies and to give us ideas of their fine structure, we must be content to be ignorant of their properties and ways of operation, being assured only of what we can learn from a few experiments. And what we can learn for sure in that way is limited indeed." [[CiteRef::Locke (2015d)|p. 212]] In making this case about the limits of our knowledge of a corpuscular world, Locke nonetheless felt confident in relying on the corpuscular hypothesis itself "because that’s the theory that is thought to go furthest in intelligibly explaining those qualities of bodies; and I fear that the human understanding hasn’t the power to replace it..." [[CiteRef::Locke (2015d)|p. 208]] While knowledge of real essences, was, for the most part, inaccessible to humans, Locke imagined that it was not inaccessible to other epistemic agents with different or more acute senses, such as God, the angels, and the inhabitants of other planets. [[CiteRef::Kochiras (2014)]][[CiteRef::Locke (2015d)|p. 211]]  Locke supposed that human knowledge was limited to what he called '''sensitive knowledge'''; knowledge of nominal essences that comes every day within the notice of our senses.[[CiteRef::Kochiras (2014)]][[CiteRef::Osler (1970)]]