Semantic Information

in logic, a measure of the content conveyed in a message. There are various approaches to the measurement of the semantic information. According to Y. Bar-Hillel of Israel and R. Carnap of the USA, a message is understood as a propositional formula (statement), and the semantic information is measured by the number of states of the universe for which this formula is false. This realizes G. W. von Leibniz’ idea that logically valid statements, true in all possible worlds, cannot carry factual information. A. A. Kharkevich suggested measuring the value of information by the change in the probability of attaining a certain aim when that change arises as a result of a given message.

The semantic information of any kind of message may be evaluated as the degree of change in the system of information (the thesaurus) of the addressee when a given message is received. Because this measure evaluates simultaneously the newness and accessibility of a message with regard to a given addressee, such a treatment of semantic information is pragmatic to a considerable degree. The sender of a message also receives semantic information, describable as new knowledge that he comes to possess about the states of the thesauri of the addressees.