categorical system

…question whether a system is categorical—that is, whether it determines essentially a unique interpretation in the sense that any two interpretations are isomorphic—may be explored. This semantic question can to some extent be replaced by a related syntactic question, that of completeness: whether there is in the system any sentence…

…an infinite model can be categorical or such that any two models of the theory are isomorphic (i.e., matchable in one-to-one correspondence), because models of different cardinalities can obviously not be so matched. A natural question is whether a theory can be categorical in certain infinite cardinalities—i.e., whether there are…

…models and is, therefore, not categorical. This applies, in particular, to the aforementioned theories T_a and T_b of arithmetic (based on the language of N), the natural models of which are countable, as well as to theories dealing with real numbers and arbitrary sets, the natural models of which are…