Absolute Infinite
The Absolute Infinite is infinity" that transcends the transfinite numbers. Cantor linked the Absolute Infinite with God.^{[1]} He held that the Absolute Infinite had various mathematical properties, including the reflection principle which says that every property of the Absolute Infinite is also held by some smaller object.^{[2]}
Cantor's view
Cantor is quoted as saying:
The actual infinite arises in three contexts: first when it is realized in the most complete form, in a fully independent otherworldly being, in Deo, where I call it the Absolute Infinite or simply Absolute; second when it occurs in the contingent, created world; third when the mind grasps it in abstracto as a mathematical magnitude, number or order type.^{[3]}
Cantor also mentioned the idea in his letters to Richard Dedekind (text in square brackets not present in original):^{[6]}
The BuraliForti paradox
The idea that the collection of all ordinal numbers cannot logically exist seems paradoxical to many. This is related to Cesare BuraliForti's "paradox" which states that there can be no greatest ordinal number. All of these problems can be traced back to the idea that, for every property that can be logically defined, there exists a set of all objects that have that property. However, as in Cantor's argument (above), this idea leads to difficulties.
More generally, as noted by A.W. Moore, there can be no end to the process of set formation, and thus no such thing as the totality of all sets, or the set hierarchy. Any such totality would itself have to be a set, thus lying somewhere within the hierarchy and thus failing to contain every set.
A standard solution to this problem is found in Zermelo's set theory, which does not allow the unrestricted formation of sets from arbitrary properties. Rather, we may form the set of all objects that have a given property and lie in some given set (Zermelo's Axiom of Separation). This allows for the formation of sets based on properties, in a limited sense, while (hopefully) preserving the consistency of the theory.
While this solves the logical problem, one could argue that the philosophical problem remains. It seems natural that a set of individuals ought to exist, so long as the individuals exist. Indeed, naive set theory might be said to be based on this notion. Although Zermelo's fix allows a Class (set theory) to describe arbitrary (possibly "large") entities, these predicates of the metalanguage may have no formal existence (i.e., as a set) within the theory. For example, the class of all sets would be a proper class. This is philosophically unsatisfying to some and has motivated additional work in set theory and other methods of formalizing the foundations of mathematics such as New Foundations by Willard Van Orman Quine.
See also
Notes
 ^ §3.2,
 ^ Infinity: New Research and Frontiers by Michael Heller and W. Hugh Woodin (2011), p. 11.
 ^ Quoted in Mind Tools: The Five Levels of Mathematical Reality, Rudy Rucker, Boston: Houghton Mifflin, 1987; ISBN 0395383153.
 ^ Gesammelte Abhandlungen mathematischen und philosophischen Inhalts, Georg Cantor, ed. Ernst Zermelo, with biography by Adolf Fraenkel; orig. pub. Berlin: Verlag von Julius Springer, 1932; reprinted Hildesheim: Georg Olms, 1962, and Berlin: SpringerVerlag, 1980, ISBN 3540098496.
 ^ The Rediscovery of the CantorDedekind Correspondence, I. GrattanGuinness, Jahresbericht der Deutschen MathematikerVereinigung 76 (1974/75), pp. 104–139, at p. 126 ff.
 ^ Gesammelte Abhandlungen,^{[4]} Georg Cantor, ed. Ernst Zermelo, Hildesheim: Georg Olms Verlagsbuchhandlung, 1962, pp. 443–447; translated into English in From Frege to Gödel: A Source Book in Mathematical Logic, 18791931, ed. Jean van Heijenoort, Cambridge, Massachusetts: Harvard University Press, 1967, pp. 113–117. These references both purport to be a letter from Cantor to Dedekind, dated July 28, 1899. However, as Ivor GrattanGuinness has discovered,^{[5]} this is in fact an amalgamation by Cantor's editor, Ernst Zermelo, of two letters from Cantor to Dedekind, the first dated July 28 and the second dated August 3.
Bibliography
 The role of the absolute infinite in Cantor's conception of set
 Infinity and the Mind, Rudy Rucker, Princeton, New Jersey: Princeton University Press, 1995, ISBN 0691001723; orig. pub. Boston: Birkhäuser, 1982, ISBN 3764330341.
 The Infinite, A. W. Moore, London, New York: Routledge, 1990, ISBN 0415033071.
 TractatusSet Theory, Skolem's Paradox and the , A. W. Moore, Analysis 45, #1 (January 1985), pp. 13–20.
