Morley conjectured that if an infinite first-order theory T is categorical in the power |T| > ℵ0, then it has a model of power < |T| Here we affirm this conjecture for the case |T|ℵ0=|T|.

Summary We have considered complete consistent systems in the first‐oder predicate calculus with identity, and have studied the set of the models of such a system by means of the maximal consistent condition‐sets associated with the system. The results may be summarized thus: (a) A complete consistent system is no‐categorical (= categorical in the denumerable domain) if and only if for every n, the number of different conditions in n variables is finite (T10). (b) If a complete consistent system has (...) a model M with finite character (i.e. a model M such that every maximal consistent condition‐set satisfied in M has a finite basis), then this model M is uniquely characterized by the property that every other model is an arithmetic extension of M (T 5). (c) Every complete consistent system, which has only a denumerable number of different associated maximal consistent condition‐sets, has a model with finite character (T8). (shrink)

In this paper we continue our study, begun in [5], of the connection between ultraproducts and saturated structures. IfDis an ultrafilter over a setI, andis a structure, the ultrapower ofmoduloDis denoted byD-prod. The ultrapower is important because it is a method of constructing structures which are elementarily equivalent to a given structure. Our ultimate aim is to find out what kinds of structure are ultrapowers of. We made a beginning in [5] by proving that, assuming the generalized continuum hypothesis, for (...) each cardinalαthere is an ultrafilterDover a set of powerαsuch that for all structures,D-prodisα+-saturated. (shrink)