The secondary literature on Aristotle’s practical philosophy is massive. A great number of illuminating studies have been provided on practical reasoning, deliberation, choice vel decision, the so-called practical syllogism, as well as legislation and political authority. All of these are key notions in Aristotle’ ethics and politics and somehow related to the concept of rule and the act of prescribing a particular action or a line of conduct. Besides, Aristotle’s treatment of the modalities and causes of human behaviour arguably implies the possibility of codifying types of action and establishing, to a certain extent, regular and constant rules of conduct. Human “movement” is a very special kind of animal movement, in that it is dominated by “practical calculation”, i.e. weighing several opportunities, evaluating situations and circumstances, imagining the future.

Nonetheless, the question of rule-making in Aristotle’s practical philosophy has not received the attention it deserves. It is widely believed that Aristotle was only concerned, at the most, with decision-making, meant as a general psychological process that enables man to arrive particular and contingent choices (or decisions). In my opinion, rule-making firmly underpins Aristotle’s ethical and political texts. Defining a rule means indicating a course of action to solve a practical problem and to get a clear aim. This course of action has to be both sufficiently specific to meet situational difficulties, and sufficiently general and constant over time to offer a code of behaviour to be used in similar situations. Furthermore, when we establish rules and prescribe them, we demonstrate the ability of directing not only our own life but also, more importantly, other people’s lives. In the latter case, we assume ends which are not of our immediate concern, in the same way that a doctor is concerned only with others’ health. My thesis is that Aristotle has deeply reflected on this problem, distinguishing rules and prescriptions from individual, episodic choices and decisions, and admitting a prescriptive reasoning which is formally equal to any syllogism, but substantially different from a scientific explication. Prescriptive reasoning does not aim at explaining a fact or an action, while revealing its final cause and agent’s intention; prescriptive reasoning is a special kind of reasoning which indicates the best thing to do (the most feasible, or the most honorable, depending either on the quality of the end for the sake of which an action is to be pursued, or on the circumstances).

Some recent scholars attribute to Aristotle the idea that action is mainly the result of experience and sensibile understanding of every contingent situation. From such a standpoint, Aristotle would be a “particularist” philosopher. My aim is to show that Aristotle, on the contrary, has recognized the need for codifying practical rules which, although pertinent to instable and accidental reality, may be sufficiently constant over time. Aristotle is at least in part induced to think about the need for both stable and flexible rules by the celebrated criticisms Plato addresses to the “written law”, i.e. political law. But what characterizes Aristotle’s reflection about prescription is his enlarging the horizon of investigation. The prescriptive limits Plato recognizes to the written nomos—its generality with respect to different situations and human characters; its fixity with respect to changing circumstances—lead Aristotle to a total rethinking of the prescriptive issue in order to grasp its foundations in the conception of deliberate choice, the theory of reasoning, and that of the structure of human soul. My intention is precisely to bring to light that the premises of Aristotle’s notion of political and legislative prescription reside in some of the fundamental parts of his practical philosophy. At least two factors emerging from the inquiry seem to have confirmed my working hypothesis. First, the possibility that deliberation, which is a heuristic search for the means to an end and a kind of hypothetical reasoning, can be converted into a deduction, that is, into a syllogism. This syllogism may be defined as prescriptive because it is able to deduce a choice, or decision, from a premise expressing either a desired end or an agreed norm, so revealing in the conclusion the appropriate action to the end. Second, Aristotle admits that, although human action is caused by desire, it is possible to deliberate about the means to an end without the desire for that end being in act. Deliberating subjects may both (a) consider an end which is not object of their own actual desire as desirable by someone else or in given situations, thus reasoning about the appropriate means to it and without coming to an action; and (b) consider a certain purpose for which it is necessary to deliberate, as an intermediate step to achieving a higher end. In both cases, deliberating subjects may prescribe for other people the performance of what they, and not those other people, have deliberated. This is the proper work of legislators when deliberating and prescribing particular rules of conduct for the sake of particular ends in various fields of social life. They do not actually desire those ends for the sake of which they prescribe. They desire in act just the ultimate end, the common good, and consider the ends for the sake of which they prescribe as the intermediate stages and instrumental conditions in view of the ultimate end. Prescription as guiding own and others’ individual actions provides the model for rule-making at the level of society and political community.