 The formal details of classical information theory turn on the probability calculus. These details may be left aside here, as the obvious conceptual point is that logical truths have a truth-likelihood of 1, and therefore an information measure of 0. Bar-Hillel and Carnap did not take this to mean that logical truths, or deductions, were without information yield, only that their theory of semantic information was not designed to capture such a property. They coined the term psychological information for the property involved. See Floridi (2013) for further details. 