IV. Psychological Presupposition of Smith’s Scientific Method

Smith’s preoccupation with taste as a main criterion by which to appraise a system of thought derives in large part from his close association with David Hume (d. 1776).  Even during his student days at Oxford, Smith bad been reprimanded for reading Hume’s Treatise of Human Nature, ⁷ and at a much later period he speaks of Hume as “by far the greatest philosopher of his age.” ⁸  Over a period of more than twenty years, Smith and Hume had been accustomed to read each other’s manuscripts and to discuss their conclusions prior to publication.  Hume’s skeptical position with regard to any certainty of knowledge about the external world is well summarized in the following quotation: “Tis not solely in poetry and music we must follow our taste and sentiment, but likewise in philosophy... reason is and ought only to be the slave of the passions.” ⁹

Although Adam Smith’s views of epistemology are revealed only by occasional comments, these suffice to establish that at least in his earlier years he shared the skeptical metaphysical views of Hume.  These include a belief that causal connections, however well substantiated they might seem in practice, have their existence only in the imagination which attributes external reality and necessity to certain configurations of events which normally occur in a given sequence.  Typical of Smith’s position is the following passage from the History of Astronomy:

Even we, while we have been endeavouring to represent all philosophical systems as mere inventions of the imagination, to connect together the otherwise disjointed and discordant phaenomena of nature, have insensibly been drawn in, to make use of language expressing the connecting principles of this one, as if they were the real chains which Nature makes use of to bind together her several operations.  Can we wonder then, that it (Newton’s System) should have gained the general and complete approbation of mankind, and that it should now be considered, not as an attempt to connect in the imagination the phaenomena of the Heavens, but as the greatest discovery that ever was made by man, the discovery of an immense chain of the most important and sublime truths, all closely connected together, by one capital fact, of the reality of which we have daily experience. ^l

Smith’s view seems to be that all causal relationships are metaphysical; the phenomena which they relate are known empirically,

7. Rae, op. cit., p. 24.

8. The Wealth of Nations, V, V, 3, p. 472.

9. David Hume, “Treatise of Human Nature,” from Hume, Works (London: Green & Grose, 1898), II, 195-98.

1. History of Astronomy, op. cit., pp. 189-90.

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but any explanation of these phenomena must make use of metaphysical concepts that reflect the outlook of a given age and a particular school of thought. ²  Smith likens science or philosophy to the effort of a person attending a stage play to imagine what stage effects behind the scene might be the causes of the visible changes; or to the reasonings of the spectator at an unfamiliar card game who undertakes to discover the rules of the game merely by observing the cards which are played in silence. ³  This concept of a scientific system as an imaginative construct intended to explain otherwise chaotic and discordant phenomena bears a striking resemblance not only to the thought of David Hume, but also to the views expressed in more recent times by Albert Einstein:

Science is not just a collection of laws, a catalogue of unrelated facts.  It is a creation of the human mind, with its freely invented ideas and concepts.  Physical theories try to form a picture of reality and to establish its connection with the wide world of sense impressions.  Thus the only justification for our mental structures is whether and in what ways our theories form such a link. ⁴

V. The Selected Analogy as the Organizing Principle of a Science

A student of the Scottish literature of Smith’s time has stated that the definition of science then required that “every system of science should possess, in order to be considered scientific at all, a general principle capable of unifying and organizing the whole mass of material. ⁵  Smith observes in the History of Astronomy that such an organizing principle for a new science has generally been selected as an analogy from some other art or science, in which a new discovery has previously been made, and has been adapted to serve as the “main hinge” for a related science.  In this way, by a process of cross-fertilization among the arts and sciences, each field has received new impetus from the application of hypotheses which, on account of their demonstrated usefulness in some other branch of knowledge, are employed experimentally in this new science.  Individuals with the “extensive” outlook of philosophers are occupied with the search for fruitful analogies which may be employed as

2. There seems to be little foundation for the position of certain American Institutionalists who would picture the Newtonian outlook as absolutist.  Smith’s Newtonian perspective was altogether relativistic.

3. History of Astronomy op. cit., pp. 74, 76-77.

4. Albert Einstein and Leopold Infield, The Evolution of Physics (New York: Simon and Schuster, 1938), p. 310.

5. Bryson, “The Comparable Interests of the Old Moral Philosophy and the Modern Social Sciences,” in Social Forces, Vol. 11 (Oct. 1932), p. 20.

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organizing principles to impart greater simplicity and accuracy to another science.  Such were the contributions of Copernicus, Descartes, and Sir Isaac Newton.

Adam Smith explains in detail the characteristics of the fruitful analogy:

Aristotle observes, that the early Pythagoreans, who first studied arithmetic, explained all things by the properties of numbers; and Cicero tells us that Aristoxenus, the musician, found the nature of the soul to consist in harmony.  In the same manner, a learned physician lately gave a system of moral philosophy based upon the principles of his own art, in which wisdom and virtue were the healthful state of the soul.... In the same manner also others have written parallels of painting and poetry, of poetry and music, of music and architecture, of beauty and virtue, of all the fine arts; systems which have universally owed their origin to the lucubrations of those who were acquainted with the one art, but ignorant of the other; who therefore explained to themselves the phaenomena, in that which was strange to them, by those in that which was familiar; and with whom, upon that account, the analogy, which in other writers gives occasion to a few ingenious similitudes, became the great hinge upon which every thing turned. ⁶

Such an analogy, in order to serve as an organizing hypothesis for a new system of science, must satisfy several requirements.  It must be simple; it must be familiar; and it must be capable of uniting the otherwise disconnected and chaotic phenomena of the field in which it is to be applied. ⁷  The propensity to wonder is natural to the human mind, and a further propensity exists to seek for a solution to the problem which gave rise to the sentiment of wonder; even a false answer, if concurred in by others, may provide satisfaction to a person who was seriously troubled by the excess of wonder. ⁸  The discovery of an apt analogy helps to restore tranquility to the mind which was once disposed to wonder, and this is the chief end of philosophy. ⁹

6. History of Astronomy, op. cit., pp. 82-84.

7. Ibid., pp. 106-9.

8. “If a person asserts anything about the moon, though it should not be true, he will feel a kind of uneasiness in being contradicted, and would be very glad that the person he is endeavouring to persuade should be of the same way of thinking with himself.”  Smith, Lectures on Justice, Police, Revenue and Arms, or,. cit., p. 171.

9. “Nothing can more evidently show, how much the repose and tranquility of the imagination is the ultimate end of philosophy, than the invention of the Equalizing Circle.... These philosophers transported themselves, in fancy, to the centres of these imaginary circles, and took pleasure in surveying from thence, all those fantastical motions, arranged, according to that harmony and order, which it had been the end of all their researches to bestow upon them.  Here, at last they enjoyed that tranquility and repose which they had pursued through all the mazes of this intricate hypothesis; and here they beheld this, the most beautiful and magnificent part of the great theatre of nature, so disposed and constructed.” History of Astronomy, op. cit. pp. 80-81.

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VI. Smith’s “Moral Newtonianism” and “Historical Aristotellianism”

Having selected an hypothesis or organizing principle for a science, the philosopher then proceeds to explain in terms of this principle the causal relationships that exist within his field.  The composed and orderly system that is thus constructed will be an imaginary machine, responding with maximum elegance and efficiency to the impulse of the great hinge or the main principle, which must control all its divergent wheels and motions:

Systems in many respects resemble machines.  A machine is a little system, created to perform, as well as to connect together, in reality, those different movements and effects which the artist has occasion for.  A system is an imaginary machine invented to connect together in the fancy those different movements and effects which are already in reality performed.  The machines that are first invented to perform any particular movement are always the most complex, and succeeding artists generally discover that, with fewer wheels, with fewer principles of motion, than had originally been employed, the same effects may be more easily produced.  The first systems, in the same manner, are always the most complex, and a connecting chain, or principle, is generally thought necessary to unite every two seemingly disjointed appearances; but it often happens, that one great connecting principle is afterwards found to be sufficient to bind together all the discordant phenomena that occur in a whole species of things. ^l

The imaginary machine that is thus constructed must have as its main hinge an analogy or hypothesis which is generally familiar, and which will impart greater simplicity to the system:

Philosophy is the science of the connecting principles of nature.... By representing the invisible chains which bind together all these disjointed objects, (it) endeavours to introduce order into this chaos of jarring and discordant appearances, to allay this tumult of the imagination, and to restore it, when it surveys the great revolutions of the universe, to that tone of tranquility, and composure which is both more agreeable in itself, and most suitable to its nature.... No system, how well soever in other respects supported, has ever been able to gain any general credit on the world, whose connecting principles were not such as were familiar to all mankind. ²

Two analogies appear to dominate the arrangement of the materials in the Wealth of Nations.  The first of these is Newtonian in origin, and the second is adapted from the Aristotelian concept of Natural Teleology, or of a Purposeful Nature.  Adam Smith was one of the few economists who experienced some success in integrat-

1. Ibid, p.116.

2. Ibid, pp.80-82.

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ing a systematic analysis of economic phenomena with an additional perspective of historical development.

Sir Isaac Newton had suggested, some decades before Smith, that his own mechanical perspective be adapted to the social sciences, stating in the first edition of the Principia:

I wish we could derive the rest of the phenomena of Nature by the same kind of reasoning from mechanical principles, for I am induced by many reasons to suspect that they may all depend upon certain forces by which the particles of bodies, by some causes hitherto unknown, are either mutually impelled toward one another, and cohere in regular figures, or are repelled and recede from one another. ³

And at the end of the Opticks, Newton added that “if natural philosophy in all its parts, by pursuing this method, shall at length be perfected, the Bounds of Moral Philosophy will also be enlarged.”⁴

Smith, in his two most important works, appears to have taken his main hypothesis, or his analogy, from the Newtonian principle of attraction.  In both the Theory of Moral Sentiments and the Wealth of Nations, the structure of the system is constituted by an equilibrium between the individual and society.  In the Theory of Moral Sentiments, sympathy serves as the regulating force which sustains the divergent motions of individuals and directs their courses within the harmonious pattern established by nature. ⁵  This is noted by Hume, who, shortly after the completion of this work, wrote to Smith: “I wish you had more particularly and fully proved that all kinds of sympathy are agreeable.  This is the hinge of your system, and yet you only mention the matter cursorily.” ⁶

In the Wealth of Nations, Smith’s ruling principle is “the desire of bettering our condition, a desire which, though generally calm and dispassionate, comes with us from the womb, and never leaves us until we go into the grave.” ⁷  Smith had explained in the Theory

3. Isaac Newton, Principia (Motte’s Translation), Preface.

4. Isaac Newton, Opticks, III, 1, qu. 3.

5. Various suggestions have been made to explain the origin of Smith’s concept of sympathy, or of its use as the organizing principle for his system of ethics.  Smith himself acknowledges that he employs the term sympathy in an unusual sense, more akin to the Greek root-word than to the word in its modern usage.  “Pity and compassion are words appropriated to signify our fellow-feeling with the sorrow of others.  Sympathy, though its meaning was, perhaps, originally the same may now, however, without much impropriety, be made use of to denote our fellow-feeling with any passion whatever.”  Theory of Moral Sentiments, op. cit., I, I, i, p. 5.  One can scarcely fail to notice the mechanical aspect of Smith’s use of sympathy, as the force relating the individual to society.  The interaction between the main characters and the chorus in Greek drama has also been pointed to as an important source for Smith’s distinctive employment of the concept of sympathy.

6. Rae, op. cit. p. 145.

7. Wealth of Nations, op. cit., II, iii, p. 324.

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of Moral Sentiments that this desire, or any success in “bettering our condition,” can do nothing to increase our happiness, because “between one permanent situation and others, there was, with regard to real happiness, no essential difference.” ⁸  Yet the desire for betterment is a propensity or an instinct that is part of human nature, having been implanted within man as an artifice of Nature and as part of the beneficent process of illusion.  Under the impulse of this inescapable propensity, man is driven to creative activity and becomes an agent of nature in her effort to keep society in motion and in a gradual state of advance. ⁹  Self-interest imparts the motion to society, and sympathy directs the motion within wholesome restraints.  The goal of this process appeared to Smith to be greater refinement; that is, an increase in the variety, the beauty, and the purposeful activity of human life.  Man is thus led “to cultivate the ground, to build houses, to found cities and commonwealths, and to invent and improve all the sciences and arts which ennoble and embellish human life.” ¹

This picture differs in two important respects from the popular impression of the Wealth of Nations.  Self-interest is not extolled for its own sake, but is considered as powerful human sentiment which might be more effectively harnessed as an instrument of economic progress.  And the goal of the economic system is regarded more as progress in refinement and in creative activity than as maximizing utility in a material sense.

The second of the two analogies which dominate Smith’s works is adapted from the Aristotelian concept of natural teleology, or of a purposeful nature.  The distinction between final causes and efficient causes, which was elaborated theoretically by Aristotle, is employed in a more ambitious manner by Smith, as he distinguishes between the purpose of nature in history, and the intentions of individuals who are unaware of the true source or purpose of their instincts.  This Aristotelian distinction is expanded by Smith into a deception, or illusion theory.

Self-preservation, and the propagation of the species, are the great ends which Nature seems to have proposed in the formation of all animals.... Nature has directed us to the greater part of these by original and immediate instincts.  Hunger, thirst, and the passion which unites the two sexes, the love of pleasure, and the dread of pain, prompt us to apply those means for their

8. Theory of Moral Sentiments, op. cit., III,  iii, p. 209.

9. Ibid., IV, I, p. 263. “it is well that Nature imposes upon us in this manner.  It is this deception which rouses and keeps in motion the industry of mankind.”

1. Ibid., IV, II, pp. 263-64.

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own sakes, and without any consideration of their tendency to those beneficent ends which the great Director of Nature intended to produce by them. ²

This analogy, taken from the most commonplace observations in biology, is applied by both Smith and Montesquieu to the field of history, where it is used to justify or to explain their confidence that a progressive force exists in nature, apart from any conscious human planning. ³  Whereas Grotius and Locke had regarded nature in a static sense as a source of law, Smith’s view was that nature operated as an active force.  Smith’s typical reference is to “the natural course of things,” or “the natural order of things.”  Even when Smith refers to nature as a source of law, he refers merely to the limitations which a constant human nature or an established trend of history would impose upon the legislator. ⁴  Nature determines laws only by imposing limits, not by specifying detailed enactments.  Laws might be enacted contrary to human nature or in opposition to the course of history, but the enforcement of such laws will be difficult and will involve great social and economic waste.

Both in his outlook on historical change, and in his method of reasoning on historical subjects, Smith resembles Darwin. In a famous passage in the Wealth of Nations, Smith pictures the har­mony and progress that are in evidence when the natural human propensities are allowed to operate without artificial restraints:

Every individual necessarily labours to render the annual revenue of the society as great as be can.  He generally, indeed, neither intends to promote the public interest, nor knows how much he is promoting it.... He intends only his own gain, and he is in this, as in many other cases, led by an invisible hand to promote an end which was no part, of his intention.... By pursuing his own interest he frequently promotes that of the society more effectually than when he really intends to promote it. ⁵

2. Ibid., II, I, p. 109.

3. James Bonar, Philosophy and Political Economy (New York: Macmillan, 1893) p.163.  “There is no reason, on Adam Smith’s philosophical principles, why human society should have been deliberately contrived by its members any more than the planetary system consciously framed by its own parts.”

4. Dugaid Stewart, Account..., op. cit. liii.  Mr. Hume adds that “the policy of ancient times was VIOLENT, and contrary to the NATURAL course of things” — by which, I presume, he means that it aimed too much at modifying, by the force of positive institutions, the order of society, according to some preconceived idea of expediency; without trusting sufficiently to those principles of the human constitution, which, wherever they are allowed free scope, not only conduct mankind to happiness, but lay the foundation of a progressive improvement in their condition and in their character.  The advantages which modern policy possesses over the ancient, arose principally from its conformity, in some of the most important articles of political economy to an order of things recommended by nature.

5. Wealth of Nations, op. cit., IV, II, p. 423.

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The inclusion within his system of a concept of a purposeful nature is a feature which distinguishes Smith from the more mechanistic French economists, such as the Physiocrats - or, in a later century, Leon Walras.  Quesnay’s neglect of this dimension of nature calls for a sharp criticism from Smith:

He (Quesnay) seems not to have considered that in the political body, the natural effort which every man is continually making to better his own condition is a principle of preservation capable of preserving and correcting, in many respects, the bad effects of a political economy, in some degrees both partial and oppressive.... If a nation could not prosper without the enjoyment of perfect liberty and perfect justice, there is not in the world a nation which could ever have prospered.  In the political body, however, the wisdom of nature has fortunately made ample provision for remedying many of the bad effects of the folly and injustice of man; in the same manner as it has done in the natural body, for remedying those of his sloth and intemperance. ⁶

VII. Adam Smith’s Purpose in the Wealth of Nations

Most readers of the Wealth of Nations experience some surprise at the discovery that Adam Smith should have adhered, at least during his earlier years, to an aesthetic or to a purely analytic ideal of science.  The goals of the Wealth of Nations seem utilitarian, and a rather materialistic concept of utility appears to replace the stoic ethic which underlies the Theory of Moral Sentiments.  The transition in Smith’s thought has led some scholars to conclude that Smith the analyst had given way to Smith the reformer.

Leo Rogin, an outspoken representative of the school of thought which would characterize the Wealth of Nations as primarily normative or polemical, argues that Smith’s model has been “quite frankly employed as (an argument) for specific programs of reform.  Obviously, however, the validity of an argument must be appraised with reference to the issue to which it is addressed.” ⁷  Rogin supports this contention by citing a passage from a letter by Smith, representing the Wealth of Nations as “a very violent attack… upon the whole commercial system of Great Britain.” ⁸  Arguing that this statement implies that the Wealth of Nations was intended primarily as a pattern for social reform, Rogin asserts that Smith’s “obvious and simple system of liberty” was an ideal and normative system, having little relevance analytically.

6. Ibid., IV, IX p. 638.

7. Rogin, The Meaning and Validity of Economic Theory (New York: Harper, 1956), p.61.  Cf. Harlan McCracken, Keynesian Economics (Baton Rouge: Louisiana State University Press, 1961), p.48.

8. Scott, op. cit., p. 283.

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In presenting this thesis, Rogin maintains that to be genuinely scientific, a system must deal with “what is” rather than with “what ought to be”; and that the “questions posed... should be susceptible of solutions in which adequately trained people will ultimately acquiesce.”  The system that is presented “must conform to the necessities imposed by persistently effective matters of fact.” ⁹  Measured by these criteria, Rogin concludes that the Wealth of Nations fails to qualify as an “objective” or a “scientific” work, and must therefore be classified as “normative economic theory.”

This characterization of the Wealth of Nations is one which cannot be refuted completely or easily, but which calls for some important qualifications.  The first of these is that the fundamental value judgment found in this work is the very broad proposition that “consumption is the sole end and purpose of all production.”¹  A misconception which must be dispelled is that some other principle, such as laissez faire or competition is Smith’s implicit norm or goal.  These are, in fact, only subordinate or instrumental elements in Smith’s system.  His espousal of the material well-being of the common people is the revolutionary normative judgment that distinguishes the Wealth of Nations from the History of Astronomy.

A more important misconception regarding Smith’s purpose is that his adherence to a simple and elegant system is an expression of contempt for the facts pertaining to the subject.  Actually, Smith’s own account of his reasons for employing a simple system seem adequate and convincing.  To have incorporated all observed facts within this field of study would have complicated the system needlessly and would have been a methodological regression in terms of Smith’s philosophy of science.  Smith therefore seemed willing to abstract from the random elements of history so as to construct a system that would provide a simple representation of its essential features.  So decisive was the impact of the Newtonian methodology, that Dugald Stewart remarks with reference to Smith’s procedure: “It is of more importance to ascertain the progress that is most simple, than the progress that is most agreeable to fact.” ²

Two other aspects of Smith’s thought should also be taken into consideration as explanations of the apparently ideal or metaphysical element in the Wealth of Nations.  Stewart makes special mention of Smith’s curiosity regarding “the principles of human nature” and the “circumstances of society.” Although Smith was

9. Rogin, op. cit., p.6.

1. Wealth of Nations, op. cit., IV viii, 625.

2. Stewart, Account ..., op. cit., xxxviii.

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not unwilling to abstract from many of the features of society, he was insistent on giving more than the usual emphasis to the logic of historical change and to the propensities of human nature.  He was not willing to restrict his speculations to economic statics or to the purely mechanical relationships of economic phenomena.

Thus we can see that the statements of Smith’s early biographers fail to bear out Rogin’s claim that Smith intended that his work be primarily normative in character.  The apparently normative aspects of the Wealth of Nations reflect Smith’s efforts to account for the trend of historical development and to do justice to the fundamental principles of psychology, ⁸ as well as to present a coherent system.  Though it cannot be denied that Smith’s “obvious and simple system of liberty” was thought of by certain statesmen of a later age as a pattern or a blueprint, it must be recognized that Smith thought of his own system as deducible from the realities of history, psychology, and logic.  The word inquiry, which is used in the title of Smith’s work, suggests likewise that its purpose was largely analytic.  The following quotation from the Account by Stewart traces more closely the relationship of the Wealth of Nations to Smith’s earlier theory of science.

In Mr. Smith’s writings, whatever be the nature of his subject, he seldom misses an opportunity of indulging his curiosity, in tracing from the principles of human nature, or from the circumstances of society, the origin of the opinions and the institutions which he describes.  I formerly mentioned a fragment concerning the History of Astronomy which he has left for publication; and I have heard him say more than once, that he had projected, in the earlier part of his life, a history of the other sciences on the same plan.  In his Wealth of Nations, various disquisitions are introduced which have a like object in view, particularly the theoretical delineation he has given of the natural progress of opulence in a country; and his investigation of the causes which have inverted this order in the different countries of modern Europe.  His lectures on jurisprudence seem, from the account of them formerly given, to have abounded in such inquiries. ⁴

It seems to have been Stewart’s view that, while the subject matter of Smith’s Wealth of Nations required some modification of the methods appropriate to astronomy, the general concept of science presented in his early writings remained substantially unchanged. ⁵

3. Ibid., liv. “The great and leading object in his (Smith’s] speculations is, to illustrate the provisions made by nature in the principles of the human mind, and the circumstances of man’s external situation, for a gradual and progressive augmentation in the means of national wealth.”

4. Ibid., xxxvi-xxxvii.

5. Stewart obviously does not accept Rogin’s criterion of the agreement of scholars as a necessary condition for scientific proof.  Both Dugald Stewart and Adam Smith believed that the collaboration of scholars was necessary for [the furtherance of knowledge, but they thought of knowledge as a dynamic process where any general consensus of scholars could not long persist. Ibid., xxxviii.] bracketed section on p.232 of original article.

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Smith’s own statements in the Wealth of Nations indicate likewise that he had not abandoned the philosophical ideals of his earlier years. ⁶  These passages imply that he still considered it the main task of philosophy to seek for the invisible chains which unite and direct the visible phenomena of nature.  Positivist scientists and philosophers have been of the opinion that the phenomena are almost self-explanatory, and that little more than a record of observations is necessary.  Smith’s view, which is expressed in his earliest writings, is that a science must explain causal relationships that are exceedingly complex, and where more than one explanation may be offered that is consistent with the observed facts. ⁷

That the subject of political economy possessed a structure of its own, and that its investigation required analytic methods distinct from those used in astronomy, Smith would be the first to concede.  The finding which is of greatest interest, however, is that Smith himself saw a close affinity between the method pursued by Newton in the study of astronomy, and the method which would be the most fruitful in political economy or moral philosophy.  It was his intention to select an analogy from the Newtonian astronomy, which might be applied as an hypothesis in the fields of moral philosophy and political economy.  According to Smith’s own outline of his material, the Wealth of Nations was to be a study in expediency, while the Theory of Moral Sentiments was to be a study in propriety.  Differences may be observed in Smith’s procedure in each of his works, attributable mainly to the great variety of subject matter; yet each of these attempts to explain a complex mass of phenomena by a few simple and familiar principles.

The features which stand out in Smith’s early delineation of the philosophy of science, and which he intended to apply in the Theory of Moral Sentiments and the Wealth of Nations, are the following:

(1) A science must be a unity.  A science or an art must grasp the essential features of its subject, and must present all parts of

6. Wealth of Nations, op. cit., V, I, p. 724.

7. Stewart, Account . . ., op. cit., xxxviii.  “When different theoretical histories are proposed by different writers, of the progress of the human mind in any one line of exertion, these theories are not always to be understood as standing in opposition to each other.  If the progress delineated in all of them be plausible, it is possible at least, that they may all have been realized; but whether they have been realized or not is of little consequence.  In most cases it is of more importance to ascertain the progress that is most simple, than the progress that is most agreeable to fact.”

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this subject as a unity that is at once elegant and harmonious.  Adam Smith gives the main credit to Descartes and to Newton for establishing this principle of unity and simplicity.

(2) The formulation of a system of science occurs through a social and historical process.  Any system of science takes shape gradually, through the common efforts of a community of scholars, but it is never complete.  Montesquieu may be regarded as the one who emphasized this evolutionary principle most effectively, while the Encyclopaedists did most to exemplify it.

(3) A science must be understood in relation to the human mind and its constitution.  It is a product both of the human mind and of the phenomena that are studied, neither of which can be regarded as passive or neutral in the creation of a science.  Any recommendations that are made through the procedures of political economy must also take account of the human mind and its natural propensities.  This is the Humean thesis.

(4) A science, like a work of art, is a means of communicating.  It will necessarily be related to the artistic taste of its creator, and it should be adapted to the understanding of the public who accept it and respond to it.  Smith seems particularly indebted to D’Alembert and Rousseau, as well as to Shaftesbury and Hutcheson, for his recognition of the aesthetic and rhetorical aspects of a system of science.

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