Practical Reason and Theoretical
Definitions And Relationships
Theoretical reason tries to assess the way things are. Practical reason decides how the world should be and what individuals should do. A theoretical proposition is good if it conforms to reality, while a practical proposition has more complicated and debatable standards, (For the idea of "direction of fit" see John Searle's 1983 Intentionality.) While practical reason decides what to do, it cannot remake reality any way it likes. The successful practical agent must take into account truths about the world. Some have inferred from this that practical reason consists largely (or entirely) in using such knowledge for practical purposes. Similarly, while theoretical reason tries to conform to the world, its proceedings are influenced by the practical needs of inquirers. Some have concluded from this that theoretical reason is the specification of the norms of practical reason to the practical project of theoretical inquiry. How individuals ought to believe is then a practical question.
Some of the interest in practical reason comes from trying to understand its failures. Theoretical irrationality is simply a mistake. But practical irrationality may invite more detailed explanations than theoretical irrationalities, because there is more to explain. (The most influential modern discussion of weakness of will is in Donald Davidson's 1980 "How Is Weakness of the Will Possible?" For Aristotle on akrasia—literally "without power over oneself," but often translated as weakness of will—see Dahl.)
Formally, there are four possible relations between theoretical and practical reason. Penetrating philosophers cannot always be so easily categorized, but these possibilities set the agenda for philosophers trying to understand the relation between theoretical and practical reason.
First, in Plato's representation of Socrates, theoretical and practical reasoning are only superficially distinct. Truth and goodness are convertible, as are the modes of reasoning that lead to apprehension of truth and goodness. To know the good is to desire it. The good life is the philosophical life, characterized not by knowledge but by eros. Anyone who fully understands the good must try to achieve it; no one can know the better, yet choose the worse. Vice is a practical form of ignorance.
Second, theoretical reasoning is a form of practice, judged by practical standards of effectiveness, appropriateness, and productivity. This position has reappeared in history under different names—sophism among the Greeks, humanism in the Renaissance, and now pragmatism and anti-foundationalism. The myth of Prometheus that Protagoras recounts to Socrates in Plato's Protagoras sees that the only difference between the knowledge of justice and piety and the knowledge embodied in the arts is that practical reason is universally distributed, while the arts are more specialized. Thomas Hobbes (1588–1679) and Giambattista Vico (1668–1744) stress, in different ways, that one can only know what one has made. Theory is a moment in practice, sometimes a means of avoiding action and sometimes a means of domination. Theoretical reasoning is what happens to practical reasoning when one temporarily abstracts from the usual conditions of practical decision—limited information, time constraints, a need to be responsive to desires and opinions, even those that are not well-grounded. Max Weber's essay, "The Profession and Vocation of Politics," can be taken as an exemplar of this version of theory and practice. Practical reasoning, for Weber, requires a distinction between an ethics of conviction—which too closely mirrors theoretical reasoning—and an ethics of responsibility. If the virtuous do not teach virtue, maybe the fault lies in their teaching ability, not in their virtue. If reason does not always rule, maybe it shouldn't—maybe the competing claims of tradition or emotion should prevail.
Third, practical reason is the application of theoretical reasoning and its conclusions to concrete, practical situations. Even theoretical reasoning needs practical judgment to reach definite conclusions. Practical reasoning is instrumental, calculating how to achieve an end that is not itself rationally determined. To be practically rational is intelligently to pursue one's interest. "Reason is, and ought only to be, the slave of the passions" (Hume, p. 415), and it is not irrational to "prefer the destruction of the whole world to the scratching of my finger" (p. 416). If reason is a slave of the passions, then practical reasoning is simply the name for reasoning that concerns itself with desires and the means of satisfying them. Practical reasoning does not differ from theoretical reasoning except in content: it is reasoning that is about preferences, desires, obstacles, and resources. If good people do not teach virtue, it is simply because they choose not to pass on their cleverness; virtue is taught by conditioning or persuading people to desire and take pleasure in the right things. This conception of the relation of theoretical to practical reason can argue that it is only through progress in the sciences that the emergence of democracy and human freedom can take place. The more one can calculate, the less one has to argue. But there is a problem within this line of thought. Without objective ends, goals are not rationally justified. Therefore, only means are justified and rational. But only ends motivate. This leaves a gap between justification and motivation. Sensing that gap, Jean-Jacques Rousseau (1712–1778) sets a new problem for practical reason when he asks how a free act of will can create obligations: what motivation could a free being have for entering a world in which he must justify what he does?
Finally, practical and theoretical reasoning are distinct forms of reasoning. Science and practical wisdom are irreducible to each other, and each, in its own sphere, gives orders to the other. In Aristotle, politics decides which sciences are studied but metaphysics determines truths according to which practice operates. Political science "prescribes which of the sciences ought to be studied in cities" (Ethics, I.2). "Phronesis is not in authority over wisdom or the better part of the intellect, any more than medical science is in authority over health. Medical science does not control health, but studies how to procure it; hence it issues orders in the interests of health, but not to health" (Ethics, VI.13). Aristotle also takes up Socrates' challenge that knowing the better yet choosing the worse is impossible, and provides (Ethics, VII) logical and physical explanations for akrasia.
Aristotle argues that practical reasoning infers in the opposite direction from both theoretical reasoning and the deliberation involved in productive activity. In the arts, barring chance, the inference from product to artist is secure: looking at a painting can tell the observer if it was skillfully produced, while courageous or just acts do not always indicate the presence of a virtuous agent. On the other hand, a virtuous person can be counted on to act virtuously; the virtuous person, unlike the artist, cannot say, "I could have acted virtuously but I didn't want to." The virtues are not rational in that way.
Immanuel Kant (1724–1804), too, sees both theoretical and practical reason as supreme, each in their own way. He states that everything acts according to laws, but "only a rational being has the capacity of acting according to the conception of laws, that is, according to principles" (Critique of Pure Reason, G412). Practical reason understands laws of freedom. In Kant, theoretical reason has priority because it can have knowledge where practical reason merely has conviction and belief. At the same time, practical reason has priority because the knowledge of theoretical reason is only knowledge of phenomena—how things appear to us—while practical reason orients itself to things as they really are. Moreover, even theoretical reason depends on practical reason, since Kant insists that "reason has no dictatorial authority; its verdict is always simply the agreement of free citizens" (A738–9/ B766–67).
Kant's "critical philosophy" asks how both theoretical and practical reason are possible. It takes for granted the existence and successful operations of theoretical reason in the sciences, and thus the Critique asks for the conditions that could justify this use of reason. At the same time, the Critique exposes as empty the claims of theoretical reason to transcend the empirical conditions that make scientific knowledge possible. The situation for practical reason is different. It cannot take some existing practices of practical reason as data to be explained. It is only by transcending the empirical conditions that limit practical reason to an instrumental role that one discovers, in pure practical reason, the legitimate moral employment of rationality. It is known that desires cause actions. Kant asks whether reason can lead to action on its own, and not only concludes that it can, but argues that actions caused by reason alone are identical with morally good acts.
For a final example, John Stuart Mill begins Utilitarianism (1863) by noticing this difference between theoretical and practical reasoning: "Though in science the particular truths precede the general theory, the contrary might be expected to be the case with a practical art, such as morals or legislation. All action is for the sake of some end, and rules of action, it seems natural to suppose, must take their whole character and color from the end to which they are subservient. When we engage in a pursuit, a clear and precise conception of what we are pursuing would seem to be the first thing we need, instead of the last we are to look forward to" (Ch. 1, para. 2).