The story of the Scottish Enlightenment dates to the rise of the individual in the Middle Ages. Benchmarks in the development of the idea of the individual include Peter Abelard’s insistence that moral responsibility only attaches to what an agent intends or to an act to which consent is given, and Thomas Aquinas’s rejection of Averroism, the idea that humans do not really have discrete minds distinct from one another but are only embodied variants of a unique, universal, and eternal mind (intellectus agens).
The Primacy of the Individual and National Improvement
With the individual fixed as part of the ontological furniture of the world, doctrines of egoism could flourish, and did so, notably in the thought of Thomas Hobbes and Bernard Mandeville. Hobbes posited intense competition between individuals and, in light of this, Mandeville recommended knavery: best to use the establishment for your own advantage for if you don’t, others certainly will, and make a fool of you in the process. His highly influential The Fable of the Bees (1705) is full of hilarious accounts of doctors, judges, generals, and priests cheating those they ought to serve.
Thinkers in 18th-century Scotland—Lord Kames, Francis Hutcheson, David Hume, Adam Smith, Thomas Reid, and Adam Ferguson, to name just the leading lights—reaffirmed natural sociality. As Kames wrote:
Nature, which designed us for society, has linked us together in an intimate manner, by the sympathetic principle, which communicates the joy and sorrow of one to many. 
Without abolishing the individual, the Scottish Enlightenment nonetheless made solidarity basic to human existence  and consciously made incursions into the scope of autonomy.
The Scottish Enlightenment was about national improvement. Great attention was given to rhetoric as these thinkers felt Scottish speech lacked the polish of English proper. Typical of 18th-century gentlemen, they traveled, but all lived principally in Scotland, and all died, and are buried, there. 
This great flourishing of ideas was also a product of the Scottish establishment; most of its leading thinkers were highly-placed jurists, university professors, and clerics of the Church of Scotland. Ferguson was chaplain to the Black Watch, one of the most storied regiments of the British Army. Hume was the least entwined with Scotland’s establishment, but not from want of trying.
The Morality and Improvement of Society
The objects of their studies also evince a deep interest in society. Credit is given Kames as an originator of anthropology, Ferguson sociology, and Smith economics. Hume was known principally as a philosopher, though he made himself a rich man by writing his massive but very popular History of England, writing it while serving as the librarian of the Advocates’ Library in Edinburgh, with access to 30,000 books.
Smith expands this into the powerful principle that a spectator monitors social and moral interactions.
Abelard’s principle that moral responsibility attaches to consent and autonomous decision was a particular target of Smith’s. He affirms the justness of the idea in the abstract; but in particular, concrete cases, it does not hold true. Here, Smith shows an interest in observation and in ordinary moral understanding that is typical of the Scottish Enlightenment, whose nickname, after all, was the School of Common Sense.
Smith points out that it is common practice to hold inanimate objects responsible for evil. You stub your toe and in revenge, you kick the offending object. Delving into legal history, he finds, among numerous examples, the trial of an ax in ancient Athens. The offending object, once found guilty, was carried to the sea with great ceremony and tossed into the waves. This is a case of deodand—things malign given into the care of God. The practice survives today. The houses of serial killers are routinely bulldozed, as are school buildings where mass shootings have happened.
Smith expands this into the powerful principle that a spectator monitors social and moral interactions. All of us, and objects, too, are inescapably linked through communal judgments. Kames elaborated on this as well:
Naturally we have a strong desire to be acquainted with the history of others. We judge of their actions, approve or disapprove, condemn or acquit ... We enter deep into their concerns, take a side. 
Our moral responsibility is determined for us by others. Reid introduced this idea into his epistemology: Our sensations relay information about the world like witnesses at court holding persons to a common standard of judgment.
Smith exhaustively explores the role of the spectator: How many spectators are there assessing us, in what do they consist, and what happens if they disagree? Smith acknowledges significant variation in the judgments of the spectator but the basic structure is invariant.
Like Smith, Hume thought commercial life a natural state.
His teacher at Glasgow was Francis Hutcheson. Hutcheson stressed the geometry of moral judgment, arguing that symmetry is basic to ethics. Smith’s formulation of this idea is that a person is moral if a spectator can role-play her situation and find proportionate the same sentiments she discloses. This harmony of sentiment is sympathy, and this is what it means to be judged as ethical.
Hume is typically portrayed as a radical skeptic, an advocate of contracts and a conception of individual autonomy that are supposedly at odds with the idea of natural sociality. This is how Reid viewed Hume, but Smith thought this a significant misunderstanding of his close friend.
Like Smith, Hume thought commercial life a natural state. That man is a “variable creature” is evident from Sparta, but, contends Hume, the decorative, ornamental life—and the commerce necessary to support it—is “the ordinary course” of human existence, and for this reason, he thought Sparta unnatural. 
According to Smith, the reason commerce is a natural state is derived from Hutcheson’s insight into the place of geometry in our moral psychology. Emotions like joy and grief build symmetry between people. Smith calls these the social or musical emotions. Anger and resentment are discordant and asymmetrical, and these he classifies as the unsocial emotions. Business is about aligning products with customers. With profound insight, Smith observes that riches are complex systems that inspire “a thousand agreeable ideas.” 
This fantasy of a life of joy, bathing in the complex symmetries of machines—watches, cars, designer kitchens, smartphones, and robots—drives the economy:
Tis the introduction of commerce or at least of opulence which is commonly the attendent of commerce which first brings on the improvement of prose. Opulence and commerce commonly precede the improvement of arts, and refinement of every sort. 
Hutcheson, Reid, and Ferguson were Protestant clergymen, and one might expect them to dissent from Smith and Hume’s defense of luxury. However, it is clearly from Hutcheson that Smith derives his argument. 
Reid was critical, staying close to the ancient and medieval worries about luxury. Ferguson shared some of Reid’s worries. He was a Gaelic-speaker and closest to the clannish sensibility of the northern Highlanders whom he served spiritually in the 42nd Foot. He took from the Highlanders their warrior ethos but combined it with the refinement of Scotland’s commercial cities.
For Ferguson, the two came together in the ideal of the knight, a blending of ferocity and suavity. About this ideal, Ferguson has much to say, and he casts the knight as the shield of natural sociality. Offering a rebuke to The Fable of the Bees, Ferguson, on the cusp of the Victorian age and the last great exponent of the Scottish Enlightenment, affirms not individual autonomy but service to others.
 Henry Home, Lord Kames, Essays on the Principles of Morality and Natural Religion (Liberty Fund, 2005), p. 16.
 The judicious role government, and principally local and provincial government, can play in confirming natural sociality is nicely seen in Smith’s discussion of toll roads. See An Inquiry into the Nature and Causes of the Wealth of Nations, Volume 2 (Liberty Fund, 1981), pp. 724-31.
 The exception is Hutcheson. Born in Northern Ireland to a Scottish family, he lived much of his life in Glasgow but died whilst visiting friends in Dublin. His grave is lost as the church in Dublin where he was buried is now a pub.
 Kames, Essays on the Principles of Morality and Natural Religion, p. 17.
 David Hume, “Of Commerce,” in Essays Moral, Political and Literary (Liberty Fund, 1985), p.259.
 Adam Smith, The Theory of Moral Sentiments (Liberty Fund, 1982), pp. 182 and 35.
 Adam Smith, Lectures on Rhetoric and Belles Lettres (Liberty Fund, 1985), p. 137.
 Francis Hutcheson, An Inquiry into the Original of Our Ideas of Beauty and Virtue (Liberty Fund, 2008), pp. 76-77.
Reprinted from Law and Liberty.