'SLAVES are very seldom inventive; and all the most important improvements have been the discoveries of the freemen. In the manufactures carried out by slaves, therefore, more labour must generally have been employed to execute the same quantity of work, than in those carried on by freemen. The work of the former must, upon that account, generally have been dearer than the latter."
As an emotive argument for the abolition of slavery, it hardly ranks alongside William Wilberforce's impassioned plea in 1789 to the House of Commons where he asked honourable members to imagine the "wretches" chained and surrounded by "every object that is nauseous and disgusting".
Nor does it have the emotional impact of Lord Auchinleck's words in 1778, effectively outlawing slavery in Scotland, 29 years before the UK Slave Trade Abolition Act: "Is a man a slave because he is black?" he asked. "No, he is our brother; and he is a man, although not of our colour."
Yet could the views on the economic impact of slavery, given in 1776 by the Scottish economist Adam Smith, have played at least an equal part in swaying the argument towards the abolition of slavery?
The issue of slavery and Britain's part in it came into sharp focus this week when the Prime Minister expressed his "deep sorrow" at the sale of millions of Africans into unpaid servitude more than two centuries ago.
His words have divided the country, with some feeling they fell short of a full apology, while others believe taking the blame for actions carried out by others centuries ago is not only pointless but raises the spectre of compensation claims.
There is no doubt, however, over Britain's role in the slave trade. By the end of the 18th century British merchants were trading up to 35,000 Africans a year.
Liverpool was the great slaving city in Britain, with Bristol not far behind. And much sugar and tobacco passed through Glasgow of course.
But while they may not have had a port bustling with the dirty trade in humans, the genteel folk of Edinburgh were certainly not innocent of involvement.
An advertisement offering a 19-year-old woman and her baby boy for sale appeared in the Edinburgh Evening Courant, the forerunner of the News, on August 30, 1766. And adverts placed by masters hunting for runaway slaves were common in Scottish newspapers, threatening dire consequences to any who dared to help the absconders.
While it's impossible to say how many black slaves there were in Edinburgh, there were certainly some. Iain Whyte, author of Scotland and the Abolition of Black Slavery, says: "We can only find records for around 70 slaves in Scotland. But there clearly were slaves in Scotland. A lot were personal servants but there were also tradesmen.
"Occasionally, they pop up in records, such as a black slave called Oronoce, owned by Dowager Countess Stair in the 1740s."
And many Scots left for the West Indies to make their fortune, such as John Newlands of Bathgate.
He made his money as a plantation owner using slave labour in Jamaica and left thousands in his will to found a school in his home town. The old Bathgate Academy is now flats, but generations of West Lothian youngsters benefited from his slave money.
At one point it was calculated that a third of the plantation owners in Jamaica were Scots. Their legacies trickled back to Edinburgh in some curious ways.
According to John Cairns, professor of legal history at Edinburgh University, one ex-pat, Dr Archibald Kerr, left his Jamaican estate, with its 39 slaves, to the city's Infirmary when he died in 1750. "So a lot of poor people in Edinburgh got charitable treatment, thanks to slavery," he says.
Inveresk Lodge, now a visitor attraction, was once owned by James Wedderburn, who, with his brother John, made his fortune in the plantations of Jamaica.
Heriot-Watt University professor emeritus and race relations campaigner Geoff Palmer describes the pair as "two of the most pernicious slavers in Jamaican history".
James fathered a string of bastard children to several slave girls, and threatened one son, who had the temerity to visit his father in 1779, with jail for bothering him.
John, who brought a black slave, Joseph Knight, back to Scotland, pursued him ruthlessly through the courts when he demanded a wage and left his service when Wedderburn refused.
Ironically, it was this case which would see slavery banned in Scotland. Knight was set free with Lord Auchinleck's noble words.
But he was one of the lucky ones. "There were many apologists for slavery," says Prof Cairns. "Many thought slavery was a practical, if distasteful, necessity to cultivate the hot lands using black labour. But from about the 1770s, public opinion slowly turned against it."
There were two strands to the growing anti-slavery feeling. The first was the evangelical movement. Based on Christian belief, it said holding other humans as chattels was against God's will.
Whyte says: "Scotland was a much more religious country than England. Lawyers in the Knight case argued there was nothing incompatible about slavery and Christianity but the tide was turning." But the other side, which gave the abolitionists' case intellectual weight, were the arguments of the Enlightenment thinkers, who emphasised rational thought.
William Robertson, the principal of Edinburgh University and a renowned scholar, launched a powerful attack on slavery.
Smith's pupil, John Millar, in his book, The Origin of Distinction of Ranks in Society, followed a Smith-style argument on the economic disadvantages of slavery. "This book became very popular in a short period of time," says Prof Cairns.
But Smith was arguably the most influential Enlightenment figure. Dr Eamonn Butler, director of the Adam Smith Institute, says: "Smith did have extraordinary influence at that time - many leading figures had his book, The Wealth of Nations, including Pitt, the Prime Minister. They would have read this and been moved by it.
"The Wealth of Nations was very much a book which says we should allow people to pursue their own ends.
"Slaves couldn't acquire property. His view was that having your own property meant you could borrow, start your own business, take risks and experiment and create new things. In a slave culture if you can't acquire any capital, you will never make any economic progress, so that holds the whole society back.
"But he also described slavery as 'an unfortunate law'. He was clearly against it on moral grounds."
Whyte certainly believes that it was a combination of religion and rational thought which defeated slavery - perhaps best illustrated by a statement from Edinburgh Chamber of Commerce in 1788. He says: "The tenor of it was that even if we believed that slavery was economically beneficial, which we do not, but if we did, as men and as Christians we would still want to see it done away with."
As for Palmer, himself descended from Jamaican slaves, he doubts that Smith was actually talking about black slaves, rather the "slavery" of the common working man.
"But that abolition was down to Christian goodwill is not necessarily true - in 300 years Christianity hadn't made a difference. There were lots of other factors."
Economically, he says, slavery was becoming less worthwhile due to increasing numbers of revolts and the discovery of how to make sugar from beet.
And Palmer doesn't believe Blair should apologise: "An apology to black people is almost pointless. It takes away responsibility. It's not really very effective."
"But there are those in Scotland still reaping the benefits of slavery, while black people still have to bear the result.
"I know it was a long time ago. But if a Scottish person can feel an injustice about Culloden, what should a black person feel about slavery?"
Scotland and the Abolition of Black Slavery 1756-1838 by Iain Whyte is published by Edinburgh University Press, priced 18.99.