 Although the numerous distributive principles vary along different dimensions, for simplicity, they are presented here in broad categories. Even though these are common classifications in the literature, it is important to keep in mind they necessarily involve over-simplification, particularly with respect to the criticisms of each of the groups of principles. Some criticisms may not apply equally to every principle in the group. The issue of how we are to understand and respond to criticisms of distributive principles is discussed briefly in the final section on methodology (see  Methodology).