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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, Locke sought to replace these stringent demands with ones more compatible with the new experimental science, such as that practiced by the Royal Society. He takes knowledge to be "nothing but the perception of the connection and agreement, or disagreement and incompatibility, of any of our ideas". [[CiteRef::Locke (2015d)|p. 196]][[CiteRef::Kochiras (2014)]] Locke distinguishes between '''nominal essences''' which are the set of observable qualities we use to classify a thing, and '''real essences''' which are the causal grounds of a substance's perceivable qualities. For Locke, true knowledge in natural philosophy would be knowledge of the real essences of material substances and the necessary connections to qualities flowing from them. With such 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. But he further supposed that such knowledge was, for the most part, beyond human faculties. He wrote that "imperceptible corpuscles are But while we lack senses acute enough to discover the active parts minute particles of matter...on which depend not only all bodies and to give us ideas of bodies’ secondary qualities but also most their fine structure, we must be content to be ignorant of their natural operations. So our lack properties and ways of precise distinct ideas of their primary qualities keeps us incurably ignorant operation, being assured only of what we want to know about themcan learn from a few experiments. And what we can learn for sure in that way is limited indeed." [[CiteRef::Locke (2015d)|p. 212]] He argued this "in terms of the corpuscularian hypothesis...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]]      This however, would require knowledge of the minute corpuscular particles of matter, beyond the range of human senses. Locke believes that their there are certain epistemic agents, such as God and the angels, who that are capable of such knowledge, but that humans are not.