ABSTRACTLynne Baker's Constitution Theory seems to be the farthest-reaching and yet the most subtly elaborated antireductive metaphysics available today. Its original theoretical contribution is nonmereological theory of material constitution, which yet has place for classical and Lewisian mereology (this formalized version of Materialism). Constitution Theory hence apparently (i) complies with modern natural science, and yet (ii) rescues the concrete everyday world, and ourselves in it, from ontological vanity or nothingness, and (iii) does it by avoiding dualism. Why, then, does it meet so many opponents-or rather, why are its many opponents so stubbornly resisting the very idea of constitution, in Baker's form? One of the most resisted claims is (iii). Is unity without identity-the feature distinguishing the relation between constituting and constituted things-the only nondualist way to oppose reductionism? What would be the price to pay for unity with identity-without reduction? What I (jokingly) call the Unitarian Tradition, going back to Plato, keeps working out the original way of constructing complex object as Unity comprising Collection, as opposed to the Aristotelian suggestion of opposing Collections and Substances. For once you have split things apart ontologically, unifying them again may prove very hard task.Plato's brief discussion of the problem of complex things Theatetus 202e-205e) bequeathed to posterity challenge. Take two m and e. (Ignore in which sense of letter, type or token.) We can call these two letters plurality. Put them together. Now, how are we to conceive of the whole me, of which m and e are parts? According to first suggestion, that whole must be conceived as all of its parts - as an aggregate somehow identical to them. Another suggestion, which Plato seems to prefer, takes the whole to be distinct from its parts, and to be in sense new, further individual thing.Theatetus seems to be the birthplace of popular dictum, currently scorned by philosophers as confused or empty, according to which a whole is more than the sum of its parts. Classical extensional mereology, the theory of parts and wholes first proposed by Stanislaw Lesniewski in 1916, and restated by Leonard and Goodman (1940),1 seemed to rule out that old Platonic idea of whole as irremediably confused or vague. One of the goals of this paper is to argue that it is not.2While Plato viewed the above complex as some single form, produced out of them [the letters], having its own single nature - something different from the letters, Aristotle seemed to echo that distinction of two ways of conceiving wholes - as Collections, or as Unities - by transforming it into distinction between two different types of material objects: wholes that are merely heaps, and wholes that are bona fide substances.3This Aristotelian passage can be seen as one ideal source of Lynne Baker's Constitution Theory, the most rigorous contemporary neo- Aristotelian Metaphysics of material objects, boldly enlarging the concept of material substance and making it, at the same time, painstakingly precise. Actually, in spite of its Aristotelian account of material objects' identity and persistence conditions in terms of their primary kinds (which hence play the role of formal causes), Baker's Constitution Theory has place for parts and wholes, namely for classical mereology, since constitutors, differently from constituted objects, can be identified with mereological sums (which thereby play the role of material causes).4 Since Lewis's successful attempt at rephrasing set theory within mereology,5 in its turn presented as the metaphysics of concrete material objects (in Quinean, Goodmanian and Ockhamian spirit), mereology itself has become the conceptual frame of reductive metaphysics, pulverizing everyday material objects, persons and artifacts, down to the ultimate Stardust of which everything material is admittedly made. …