Various theorists are split as to whether the rules are the only determinant of moral behavior or not. For example, Robert Nozick held that a certain set of minimal rules, which he calls "side-constraints," are necessary to ensure appropriate actions. There are also differences as to how absolute these moral rules are. Thus, while Nozick's side-constraints are absolute restrictions on behavior, Amartya Sen proposes a theory that recognizes the importance of certain rules, but these rules are not absolute. That is, they may be violated if strict adherence to the rule would lead to much more undesirable consequences.