 The Transition Question: A central question for essentialism concerns the transition between knowledge of essence and knowledge of modality (see  question (b)  above). For deduction theories that deploy the inference from  (E1)  and  (E2)  to  (E3),  one should ask: how is the bridge-principle connecting essence to modality, (E1), known? Horvath (2014) argues that it isn’t clear how we come to know the bridge principle (E1). As Horvath remarks, a (purportedly non-modal) real definition or essence-statement (like “gold is essentially the element with the atomic number 79”) doesn’t make any explicit claim about metaphysical possibility or necessity. Because of that, definitional essences do not seem generally capable of explaining or grounding metaphysical modality. As Mackie (forthcoming) puts it: