This chapter singles out and explains one important type of rule and principle. Rules and principles of this type are normally stated by saying that a certain person ought to, should, must, etc., perform a certain action. This marks them out as practical principles and rules. The analysis is limited to ‘categorical’ rules and principles. ‘Principles’ and ‘rules’ are often used interchangeably, though the word ‘principles’ usually carries an implication of greater generality and greater importance than the word ‘rules’. Not all mandatory norms are rules or principles. Some other normative...

This chapter singles out and explains one important type of rule and principle. Rules and principles of this type are normally stated by saying that a certain person ought to, should, must, etc., perform a certain action. This marks them out as practical principles and rules. The analysis is limited to ‘categorical’ rules and principles. ‘Principles’ and ‘rules’ are often used interchangeably, though the word ‘principles’ usually carries an implication of greater generality and greater importance than the word ‘rules’. Not all mandatory norms are rules or principles. Some other normative phenomena resemble rules and principles in all respects except in being particular, and it is advantageous to treat them together. This chapter looks at four elements in every mandatory norm: the deontic operator; the norm subjects, namely, the persons required to behave in a certain way; the norm act, namely, the action which is required of them; and the conditions of application, namely, the circumstances in which they are required to perform the norm action.