 Most of the present section has focused on generalisations linking naturalness with relatively familiar, easy-to-grasp notions.  We have not yet discussed possible links between naturalness and many other “heavy duty” metaphysical notions — notions whose good standing and theoretical utility is as controversial as that of naturalness itself.  Among the notions for which such connections might be worth investigating are: essence (Fine 1994); ontological dependence (see the entry on ontological dependence); truthmaking (see the entry on truthmakers); substance (see the entry on substance); reality and factuality (Fine 2001); modes of being (explained in terms of naturalness in McDaniel 2017b, ch. 1); and degrees of being (McDaniel 2017b, ch. 7).  Space precludes a discussion of these topics.  But to convey a sense of the possibilities, let us briefly consider some possible connections to grounding, a notion that has been especially prominent in the recent metaphysics literature (for background, see the entry on metaphysical grounding). 