Abstract

In 1972,Ernst Ulrich and Christine von Weizs ¨acker introduced the concept of pragmatic information with three desiderata:(i) Pragmatic information should assess the impact of a message upon its receiver;(ii)Pragmatic information should vanish in the limits of complete (non-interpretable)'novelty 'and complete 'confirmation';(iii)Pragmatic information should exhibit non-classical properties since novelty and confirmation behave similarly to Fourier pairs of complementary operators in quantum mechanics. It will be shown how these three desiderata can be naturally fulfilled within the framework of Gardenfors' dynamic semantics of Bayesian belief models.(i)The meaning of a message is its impact upon the epistemic states of a cognitive agent. A pragmatic information measure can then be quanti .ed by the average information gain for the transition from a prior to a posterior state.(ii)Total novelty can be represented by the identical proposition, total con- .rmation by the logical consequence of propositions. In both cases, pragmatic information vanishes.(iii)For operators that are neither idempotent nor commuting, novelty and confirmation relative to a message sequence can be defined within Gardenfors' theory of belief revisions.The proposed approach is consistent with measures of relevance derived from statistical decision theory and it contains Bar-Hillel 's and Carnap's theory of semantic information as a special case.