The reason for not having formulated this measure in positive but in negative terms is Menger's view that empirical sciences and hence also the social sciences are based on observation and experience. It is impossible to observe and to measure the increase of utility given an increase in the consumption of a good by one unit, ceteris paribus; but it is possible to observe that individuals satisfy concrete wants by consuming concrete quantities of goods and that they refrain from satisfying that concrete want which for them is the least important one if the quantity of a good is reduced by one unit. Accordingly, Menger also derives the equimarginal principle from observation.