Below is a repost of my response to Leon of After Nature here. I discuss the issue of what is "irreducible," e.g., the "irreducible cores of objects" from my Dewey-Peircean perspective.
"I like irreducible cores, and think that they can do some work with respect to value. Is a core is an intensity, power, capacity – then in those respects any core has an infinite worth in its power to produce effects – some producing more or greater effects than others. So a core isn’t a cold dead center, it is an active nature that withdraws as we try to grasp it. Yet “it” is singular (I think, for now). Hopefully this makes some sense -typing during my travels."
I agree with everything you say, but let me put it in this perspective that tries to specify what is irreducible. I reject the idea that an actual event (object) "has" an irreducible core that constitutes its distinctness, and much of the argument is due to how I understand the composition/composability of powers.
An "object" may "have" irreducible cores in the sense that powers are "atomic" as are the emergent properties of actual events. The powers are irreducible to the event, and the emergent properties, e.g., created powers, are irreducible to those that constitute the actuality of the event. There's your irreducibility. However, and this might be my misunderstanding of Harman's position, the actual event (or object?) does not "possess" those powers. That whole is not a discrete unit. In sum, irreducibility is tied to either the emergence of the event, or the powers themselves, but not the actuality or "identity" of the event. Hence, given that "substance" and "identity" usually go hand-in-hand, though not if we read our Aristotle carefully, I refuse to use the term substance as it is misleading. I suspect that OOO positions differ of the proposed logical treatment of irreducibility, identity, and the fundamental unit of existence or analysis. I believe that Bryant and Harman disagree on this point, so we should not assume that there are just two positions; see my discussion with Bryant on his blog.
By the way, the hard distinction between constitutive powers of an actual event and its emergent powers is temporal; constitutive powers must be in play to constitute provide persistence for the actual event, and only afterwards do the emergent powers manifest.