Today, when we speak of measuring, of units of measure, methods of measure, or simply of magnitudes, we mean as a rule those that are already related to idealities and are exact so it is difficult for us to carry out the abstract isolation of the plena which is so necessary here:.e., to consider experimentally, so to speak the world of bodies exclusively according to the aspect of those properties belonging under the title specific sense qualities, through a universal abstraction opposed to the one which gives rise to the universal world of shapes.