Abstract
We describe some possibilities of approximations by $$\omega_{1}$$ -categorical structures and theories. The obtained results of approximations are called pseudo- $$\omega_{1}$$ -categorical. Possibilities for expansions and restrictions of theories with respect to the $$\omega_{1}$$ -categoricity and pseudo- $$\omega_{1}$$ -categoricity are studied. We describe properties and possibilities for pseudo- $$\omega_{1}$$ -categorical theories of partial orderings, whose connected components form chains. Theories of pseudo- $$\omega_{1}$$ -categorical abelian groups are described, too.