In his program-stating paper 'On the Construction of Machine Language for an Information Machine', the Soviet pioneer of information science, V. A. Uspenski [9], has specified some requirements that should be met by the information language to be used in any computerized information system. One of these requirements consists in the formalization and, therefore, in the machine solution of semantic identification, i.e. the decision whether two data, differently expressed or recorded, are identical with respect to their meaning. In the present paper the concept 'to have the same meaning' or 'to be semantically identical' is explained by such means as elaborated in the theory of semantic information and, especially, on the basis of the concept 'transmitted information'. Because of this, the concept 'information synonymy' is introduced. Since existing attempts to solve the problem of semantic identification are usually based on the Leibnizian principle of identity, we shall try to show some difficulties and limitations inherent to methods and criteria based on Leibniz' principle. Although the new concept 'information synonymy' adheres, in principle, to the scheme of requirements which are deducible from the Leibnizian principle, we shall, try to present a somewhat modified version of these requirements.
1. TRADITIONAL (LEIBNIZIAN) CRITERION OF IDENTITY AND THE PROBLEM OF SEMANTIC IDENTIFICATION
The usual formulations of the Leibnizian criterion have more general competence and do not only serve to solve the problem of semantic identification. This criterion regards as identical all entities, whether of linguistic or non-linguistic nature, which have all properties in common. Let &r denote the class of these entities and ~ the class of predicates as the names of properties assignable to the elements of~. Then in the system <~,~>, in which elements (variables) of the class 3~ are denoted by small latin letters x, y, ul, u2 and elements of the class ~ by block letters P1, 1"2, the Leibnizian criterion can be formulated in the twofold manner: