It is undoubtedly of the greatest importance to know those tools, to be able to practise those formalizations and to define the levels upon which they can be performed; it is no doubt of interest historically to know how Condorcet was able to apply the calculation of probabilities to politics, how Fechner defined the logarithmic relation between the growth of sensation and that of excitation, how contemporary psychologists make use of information theory in order to understand the phenomena of learning.