Abstractions are themselves not actual entities, but are the only entities that can be real. An abstraction is a conceptual entity that involves more than one single actual entity. Whitehead's ontology refers to importantly structured collections of actual entities as nexuses of actual entities. Collection of actual entities into a nexus emphasises some aspect of those entities, and that emphasis is an abstraction, because it means that some aspects of the actual entities are emphasised or dragged away from their actuality, while other aspects are de-emphasised. Whitehead admitted indefinitely many eternal objects. An example of an eternal object is a number, such as the number 'two'. Whitehead held that eternal objects are abstractions of a very high degree. Many abstractions, including eternal objects, are potential ingredients of processes. Relation between actual entities and abstractions stated in the ontological principle For Whitehead, besides its temporal generation by the actual entities which are its contributory causes, a process may be considered as a concrescence of abstract ingredient eternal objects. God enters into every temporal actual entity. Whitehead's ontological principle is that whatever reality pertains to an abstraction is derived from the actual entities upon which it is founded or of which it is comprised. A source of an aphorism The book is also the source of the frequently heard aphoristic reference to Western philosophy all being “footnotes to Plato": Publication data The several originally published editions of Process and Reality were from New York and from Cambridge UK. There were many textual errors, partly due to Whitehead's imperfect handwriting and lack of interest in proof-reading. A largely corrected scholarly redaction was eventually prepared and published as Process and Reality: An Essay in Cosmology (1929). 1979 corrected edition, edited by David Ray Griffin and Donald W. Sherburne, Free Press, . See also Mereotopology Michel Weber Whitehead's point-free geometry References Secondary literature Biacino L., and Gerla G., 1991, "Connection structures," Notre Dame Journal of Formal Logic 32: 242–247. Clarke, Bowman, 1981, "A calculus of individuals based on 'connection'," Notre Dame Journal of Formal Logic 22: 204–18. , 1985, "Individuals and Points," Notre Dame Journal of Formal Logic 26: 61–75. Cobb, John Boswell, Jr., Whitehead Word Book, Claremont, P&F Press, 2008. Leclerc, Ivor, Whitehead's Metaphysics, George Allen and Unwin Ltd., 1958. Lowe, Victor, 1962. Understanding Whitehead. Johns Hopkins Univ. Press. Mesle, C. Robert, 2008. Process-Relational Philosophy: An Introduction to Alfred North Whitehead, Templeton Press, 1st