Smith explains a wide range of social orders--morals, markets, laws, languages, and sciences--as spontaneous orders arising from human actions but not by human design. As James Otteson has shown, Smith's explanations of these spontaneous orders manifest an analytic model with four elements: a motivating desire, the rules developed, a currency (what gets exchanged), and a resulting unintended system of order.
Otteson argues, however, that Smith does not extend this kind of explanation to cosmic nature or human nature, which require explanation through intelligent design by God. The very possibility of unintended order presupposes a certain constitution of human nature and certain recurrent circumstances of social life--such as the natural desires that motivate spontaneous orders and circumstances such as the dependence of children on adult care. This presupposes an order of nature, including human nature, that cannot itself be explained as unintended order, because, Smith suggests, it shows evidence of intentional design by an intelligent, benevolent, and omnipotent God. Otteson can supply plenty of textual evidence for this from The Theory of Moral Sentiments, because Smith often refers to God, the Deity, or the Author of Nature as ordering nature to His benevolent ends.
There are at least three possible explanations for this theological language in Smith's writing. First, one could say, as Otteson does, that Smith was a religious believer--perhaps an orthodox Christian, or at least a Deist. Second, one could say that Smith was not a religious believer, but that he needed to feign religious belief to avoid persecution by religious zealots and to avoid offending the religious believers around him. Third, one could say that while he was not an orthodox believer in a divinely designed world, he had no alternative explanation for the appearance of design in nature, and so he was forced to use the language of divine design.
I think the second and third explanations are the most persuasive, and here my thinking has been influenced by two articles--Ronald Coase, "Adam Smith's View of Man," Journal of Law and Economics, 19 (1976): 529-46; and Gavin Kennedy, "The Hidden Adam Smith in His Alleged Theology," Journal of the History of Economic Thought, 33 (2011): 385-402.
Kennedy makes a good case for the second explanation--that Smith had to feign religious belief to avoid being persecuted or being offensive in a society where Christian orthodoxy was pervasive. Kennedy reminds us, for example, that Smith could never have been a professor at the University of Glasgow if he had not signed the the Calvinist Confession of Faith before the Presbytery of Glasgow. He also reminds us that Smith was deeply devoted to his mother, with whom he lived, and that any public questioning of religious belief would have offended her. Kennedy shows how, after his mother's death in 1784, and as he was nearing death himself, Smith made revisions to the 6th and final edition of The Theory of Moral Sentiments that eliminated or muted the more overtly theological passages of his earlier editions. Moreover, Smith's deep friendship with David Hume, who was notorious for his reputation as an atheist, and his praise of Hume as the most wise and virtuous man suggest that he shared Hume's skepticism, but that he could not be as open as Hume in expressing this in public.
All of this is evidence that Smith was a practitioner of secret writing--conveying a conventional acceptance of orthodoxy to his popular readers, while suggesting to the few careful readers that his true teaching was subversive of orthodoxy.
And yet even in the 6th edition of The Theory of Moral Sentiments, when the fear of persecution or of offending loved ones was lessened, Smith still has many passages about the divine design of cosmic nature and human nature. This might require the third explanation, which is suggested by Coase: although Smith was not a religious believer, and although he preferred to explain the world as a product of purely natural causes, he could see that human nature was well adapted to the circumstances of life in ways that were hard to explain as a purely natural product of spontaneous ordering, and consequently he was forced to use the language of divine design.
Coase notes Smith's preference for naturalistic explanations in The Wealth of Nations, where Smith writes:
"The great phenomena of nature, the revolutions of the heavenly bodies, eclipses, comets, thunder, lightning, and other extraordinary meteors; the generation, the life, growth, and dissolution of plants and animals; are objects which, as they necessarily excite the wonder, so they naturally call forth the curiosity of mankind to enquire into their causes. Superstition, first attempted to satisfy this curiosity by referring all those wonderful appearances to the immediate agency of the gods. Philosophy afterwards endeavoured to account for them, from more familiar causes, or from such as mankind were better acquainted with, than the agency of the gods. As those great phenomena are the first objects of human curiosity, so the science which pretends to explain them must naturally have been the first branch of philosophy that was cultivated. The first philosophers, accordingly, of whom history has preserved any account, appear to have been natural philosophers" (V.i.f.24, p. 767-68).The problem, however, as Coase indicates, is that in Smith's day, the science of "the life, growth, and dissolution of plants and animals" had not yet reached the evolutionary theory of Darwin that would explain the origin of species, and thus there was no good alternative to religious belief in the divinely intelligent design of the living world, including human nature.
Nevertheless, Coase recognizes that in some passages in The Theory of Moral Sentiments, Smith comes very close to the kind of evolutionary explanation that was later elaborated by Darwin. Smith identifies "self-preservation, and the propagation of the species" as "the great ends which Nature seems to have proposed in the formation of all animals" (II.i.5.6, p. 77). He stresses the instinctive bond of parents in caring for their offspring as rooted in mammalian nature (VI.ii.1.5, p. 219). And he sees how the moral sentiments as based on sympathy are adaptive for the human animal, a fundamental idea for Darwin in explaining the evolution of human morality.
We can conclude from this that in 1859, with the publication of Darwin's Origin of Species, it became possible, for the first time, to be an intellectually fulfilled Smithian liberal. Darwin's evolutionary theory made it possible to explain the biological origins of human nature as an unintended order that made possible the largely self-regulating society arising unintentionally from the free exchanges of individuals, which was the fundamental idea of Smithian liberalism.
By showing how all living species--including the human species--could have evolved naturally, without any need for special creation by God, Darwin extended the idea of unintended order to embrace the whole history of life, and thus he allowed for moral order to be understood as free-standing, as rooted in moral anthropology rather than moral cosmology, without any necessary support from a theology of intelligent design. This then made it safe for governments to tolerate religious pluralism and even atheism without fear that the moral order of society would collapse without a coercively enforced religious orthodoxy.
Related posts can be found here. and here.