Using a basic theorem from mathematical logic, I show that there are field-extensions of R on which a class of orderings that do not admit any real-valued utility functions can be represented by uncountably large families of utility functions. These are the lexicographically decomposable orderings studied in [1]. A corollary to this result yields an uncountably large family of very simple utility functions for the lexicographic ordering * Email: d.rizza@uea.ac.uk 1 of the real Cartesian plane. I generalise these results to the lexicographic ordering of R n , for every n > 2, and to lexicographic products of lexicographically decomposable chains. I conclude by showing how almost all of these results may be obtained without any appeal to the Axiom of Choice.
Non-Archimedean utility functionsUtility functions may be seen as strong homomorphisms from a complete preorder Z = Z, into a numerical ordering. Although a customary choice for the codomain of a utility function is the set R of real numbers, alternatives that violate the Archimedean property have been studied since at least the 1950's (see e.g. [6] 2 preference to be represented. In this paper I adopt this perspective on a class of linear orders that lack real-valued utility functions and show that each of them has an uncountable family of utility functions on an arbitrary, elementary extension of the real field containing positive infinitesimals. As a consequence of this result, I also establish a connection between lexicographically ordered, real vector spaces and elementary extensions of the reals, the two more prominent choices of non-Archimedean codomain for utility functions. The best known linear order from the class I consider was introduced by Debreu in [4]: it is the lexicographic ordering of the real Cartesian plane, i.e., the chain L 2 = R 2 , 2 , where the binary relation 2 is defined by the condition: r, s 2 r , s iff r < r or r = r and s ≤ s .Seen as a vector space, L 2 is non-Archimedean, since there is no positive, integer multiple of 0, 1 that is greater than 1, 0 . This suggests that a utility representation for L 2 should assign to every vector of the form 0, n a value that is infinitely close to that of 0, 0 . The same argument naturally extends to encompass the class of lexicographically decomposable chains described in [2] and studied in [1]. Since these chains are isomorphic to certain lexicographic orders, and one may regard lexicographic orders as a linear arrangement of clusters of infinitely close points, it is natural to associate them with a utility function on a non-Archimedean structure. Theorem 3.2 shows that uncountable families of such functions always exist 2 . This result locally improves in several ways the general theorem, proved by Skala in [14] and more concisely presented by Narens in [12], to the effect that every transitive and complete relation has a utility function on a particular ultrapower extension of the reals.I show in section 3 that, with regard to lexicographically decomposable chains,2 To be preci...