When one wishes to formulate, evaluate and implement public policies, the existence of a plurality of social actors, with interest in the policy being assessed, generates a conflictual situation. How such a conflict should be dealt with? This paper defends the thesis articulated in the following points: Different metrics are linked to different objectives and values. To use only one measurement unit for incorporating a plurality of dimensions, objectives and values, implies reductionism necessarily. Point can be proven as a matter (...) of formal logic by drawing on the work of Geach about moral philosophy. This theoretical demonstration is an original contribution of this article. Moreover, here the distinction between predicative and attributive adjectives is formalised and definitions are provided. Predicative adjectives are further distinguished into the new categories of absolute and relative ones. The new concepts of set commensurabi... (shrink)