In this chapter, I discuss the differences between ontic and epistemic conceptions of scientific explanation, mainly in relation to the so-called new mechanical philosophy (NMP). I emphasize that the debate on conceptions of scientific explanation owes much to Wesley Salmon’s ontic-epistemic distinction, although much has changed since his formulation. I focus on the interplay between ontic and epistemic norms and constraints in providing mechanistic explanations. My conceptual analysis serves two aims. First, it shows that both sets of norms and constraints, ontic and epistemic, are necessary for scientific theorizing. Second, it shows that there are multiple dimensions involved in scientific explanation, rather than clear-cut alternatives between ontic and epistemic aspects. I conclude the chapter with a general observation that, although contextual aspects of explanations are unavoidable, the epistemic-relativity of our categories, explanations, and models can in fact be compatible with their objectivity. Instead of making hastily drawn ontological implications from our theories or models, we should carefully scrutinize them.