  Indeed, we are able to discern necessary connections in two instances, as noted earlier. (One case involves only primary qualities— “Figure necessarily presupposes Extension” (E IV.iii.14, p. 546)—and the other involves tertiary and primary qualities—“receiving or communicating Motion by impulse, supposes Solidity” (E IV.iii.14, p. 546).) If we knew more about the primary qualities of bodies, we might multiply such instances: “And if we knew these primary Qualities of Bodies…we might be able to know a great deal more of these Operations of them one upon another.” That is, if we knew real essences, we could derive more necessary connections, knowing, for instance, the causal relation between opium and sleep, and as certainly as we now know that impulse requires solidity.