All absolute governments must very much depend on the administration; and this is one of the great inconveniences attending that form of government. But a republican and free government would be an obvious absurdity, if the particular checks and controuls, provided by the constitution, had really no influence, and made it not the interest, even of bad men, to act for the public good. Such is the intention of these forms of government, and such is their real effect, where they are wisely constituted: As on the other hand, they are the source of all disorder, and of the blackest crimes, where either skill or honesty has been wanting in their original frame and institution.I.III.4
So great is the force of laws, and of particular forms of government, and so little dependence have they on the humours° and tempers of men, that consequences almost as general and certain may sometimes be deduced from them, as any which the mathematical sciences afford us.--David Hume "That Politics May be Reduced to a Science."
At first glance, Hume is defending here a species of republicanism. But Hume's lines here were also taken to be the founding text of a normative, research program of institutional design ('wise constitution'), which takes itself to create institutions in which the incentives are such that it is in the self-interest of even bad people to promote the "public good" including ones distinct from Hume's republican commitments. This project is historically associated with a careful reader of Hume, Madison, who wrote that "if men were angels, no government would be necessary" (which echoes Spinoza's Political Treatise 6.3: "if human nature were so constituted, that men most desired what is most useful, no art would be needed to produce concord")+ and philosophically with a range of thinkers from Kant's race of "devils" all the way to Buchanan and Tullock's public choice theory. As Kant puts it in Perpetual Peace:
The problem of organizing a state, however hard it may seem, can be solved even for a race of devils, if only they are intelligent. The problem is: "Given a multitude of rational beings requiring universal laws for their preservation, but each of whom is secretly inclined to exempt himself from them, to establish a constitution in such a way that, although their private intentions conflict, they check each other, with the result that their public conduct is the same as if they had no such intentions."
A problem like this must be capable of solution; it does not require that we know how to attain the moral improvement of men but only that we should know the mechanism of nature in order to use it on men, organizing the conflict of the hostile intentions present in a people in such a way that they must compel themselves to submit to coercive laws. Thus a state of peace is established in which laws have force.
In fact, Hume need not be taken to be defending republicanism. All he is saying that republicanism would be an absurdity, in the sense of an internal practical contradiction, if one assumed that "the particular checks and controuls, provided by the constitution, had really no influence." That is, Hume is saying that even republicanism -- a normative program -- presupposes that it is empirically true that humans are responsive to systematic incentives and interests. (I leave aside here, to what degree and in what way Hume actually embraced a normative/empirical distinction.)
In the right contexts this empirical fact, that humans are responsive to systematic incentives and interests, allows one to deduce "consequences almost as general and certain" as "any which the mathematical sciences afford us." Here Hume connects his program for political science to his great program for the "science of Man" in the Introduction of the Treatise:
We must therefore glean up our experiments in this science from a cautious observation of human life, and take them as they appear in the common course of the world, by men’s behaviour in company, in affairs, and in their pleasures. Where experiments of this kind are judiciously collected and compared, we may hope to establish on them a science, which will not be inferior in certainty, and will be much superior in utility to any other of human comprehension.
Throughout Hume's philosophy he argues that his science is foundational to and more useful than the other (mathematical-empirical) sciences and just as (epistemically) secure.* So, given the tight fit between Hume's "That Politics May be Reduced to a Science" and Hume's Treatise, it stands to reason that this essay gives us a glimpse of "the examination of...politics...which will compleat" his Treatise (as the Advertisement to the Treatise promised.).
So far so good. Now consider the opening passage from Spinoza's (posthumous) Political Treatise (in the old Gosset translation with minor corrections):
3. And, certainly, I am fully persuaded that experience has revealed all conceivable sorts of commonwealth, which are consistent with men's living in concord [homines concorditer vivant], and likewise the means by which the multitude may be directed [multitudo dirigi] or kept within fixed bounds. So that I do not believe that we can by meditation discover in this matter anything not yet tried and ascertained, which shall be consistent with experience or practice. For men are so situated, that they cannot live without some general law. But general laws and public affairs are ordained and managed by men of the utmost acuteness, or, if you like, of great cunning or craft. And so it is hardly credible, that we should be able to conceive of anything serviceable to a general society, that occasion or chance has not offered, or that men, intent upon their common affairs, and seeking their own safety, have not seen for themselves.
4. Therefore, on applying my mind to politics, I used certain and undoubted reason to offer demonstratios [certa et indubitata ratione demonstrare,], or to deduce from the very condition of human nature, not what is new and unheard of, but only such things as agree best with practice. And that I might investigate the subject-matter of this science with the same free spirit [animi libertate] as we generally use in mathematics, I have laboured carefully, not to mock, lament, or execrate, but to understand human actions; and to this end I have looked upon passions, such as love, hatred, anger, envy, ambition, pity, and the other perturbations of the mind, not in the light of vices of human nature, but as properties, just as pertinent to it, as are heat, cold, storm, thunder, and the like to the nature of the atmosphere, which phenomena, though inconvenient, are yet necessary, and have fixed causes, by means of which we endeavour to understand their nature, and the mind has just as much pleasure in viewing them aright, as in knowing such things as flatter the senses.
(Reversing Spinoza order of presentation we may say that) Spinoza self-consciously sets out to offer a pleasing science of man. In this causal science there is no room for moralizing about original sin and other purported defects of human nature. Rather, Spinoza treats the passions as (hidden causal) properties of human nature from which effects can be deduced. Spinoza denies that his conclusions are original; rather they conform to existing practice. While Spinoza does not explicitly say his conclusions are as secure as other natural sciences, his choice of contrast class (meteorology) suggests he is not setting the bar beyond reach.
In fact, (moving to the third paragraph) Spinoza is explicit that he is merely conforming to, and perhaps systematizing, practical know-how [praxi -- a term that he repeats through the passage] available to (use Mandeville's term) the crafty politician, who according to Spinoza knows how to direct the multitude. (Unlike Adam Smith, who distrusted such craftsmanship, Hume praises it--recall his high praise of De Witt's ability to "manage" the Dutch and maintain a "spirit of union" or concord.] Spinoza explicitly draws on comparative institutional practices found in [historical] experience [experientiam omnia civitatum genera]. I have labeled such comparative institutional analysis, Socratic Political Theory (recall; but see, especially, this post on Ursula Le Guin and this one on Thomas More.) Such analysis is rooted in empirical experience, but itself normative (because focused on the "public good" -- Spinoza puts it in terms of "living in concord" -- and developed around, what Weber later called, ideal types of particular institution frameworks).
As an aside, I have intimated here (and elsewhere) that Hume that Spinoza would have read Spinoza's Political Treatise. This does not preclude the reality that Hume and Spinoza read the same sources (Machiavelli, especially, but also More and Bacon).
Let me wrap up. In the title of this post, and above I noted that Buchanan (a student of Knight) and Tullock's public choice theory is one of the modern heirs of this (Spinoza-Humean) Socratic political theory.** This fact is less surprising if we remember that as late as 1964 the reality of Socratic political theory kind was explicitly presupposed -- in the context of cold war rivalry -- by the Chicago economist (and also a student of Knight), George Stigler, and made conceptually possible the proper competence of the economist as such; "consists in understanding how an economic system works under alternative institutional frameworks." (Presidential Address to the American Economics Association; recall this post.) Needless to say, the contemporary mainstream economist lacks such competence nor wishes for it. If Stigler is correct, then in our life-time, a Kuhn-loss has taken place in front of our eyes. That is to say, public choice represents a vision for political economy that is rooted in older intellectual traditions. How to sort the traditional elements from the modern innovations is the topic for a series of future posts.
+The whole of Political Treatise 6.3 is relevant for what follows. See also TTP Chapter 5.
**I should say that this is more true of Buchanan, who fully embraces his own practice as a normative theorist (see his Nobel lecture) and, as I witnessed personally, in increasing Kantian terms late in life; less so of Tullock (who is less idealistic about the scientific enterprise and shares in Mandeville's unmasking spirit.).