  Sensitive knowledge is knowledge of the “effects [that] come every day within the notice of our Senses”, without an understanding of their causes; “we must be content to be ignorant of” those causes (E IV.iii.29, pp. 559–560). Instead of knowing real essences, the causal basis of the properties we perceive, we know only those perceived properties, from which we construct nominal essences. Instead of employing deduction, we are forced to rely upon “trials”—observations and induction. Instead of knowing the necessary connections holding between a substance’s real essence and its other qualities, including its tertiary qualities (which might include, recall, causal connections with substances beyond the remotest star), we know only the co-existences of properties. And from the mere, regular co-existence of properties found in observed cases, Locke observes, we could not know with certainty that the same set will be found co-existing in the next case.