SLAVERY goes far back in human history. Only in the last couple of centuries has our species come to a sort of collective decision that it no longer wishes to enslave some of its members and has taken serious steps to ban the practice – a ban that is by no means wholly effective, however, even today.

The earliest slaves we can document date to the Sumerian empire, in present-day Iraq, of 2000 BC. On a clay tablet, a victorious king inspects captured prisoners who, bound together by ropes, parade before him.

Today we are more likely to regard the ancient Greeks as our moral ancestors, but they had slaves too. It was a status the philosopher Aristotle thought “natural” – nature had decreed some people should be slaves and some free, and there was nothing more useful to be said about it. In fact, Aristotle’s fellow philosopher Plato was reduced to slavery by a king he had displeased, although he was afterwards ransomed and liberated.

Christianity is not as clear about slavery as we might assume. St Paul said that in Jesus Christ there was neither slave nor free, indicating that those of either status could be admitted into the church. But this did not mean the church called for the liberation of slaves. At least, St Paul does not say so.

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In fact, many societies kept slaves into the dawn of the modern era. It was not just a matter of Europeans holding non-white slaves. Most of these had previously been captured, and sold on, by warlike African chiefs. Islamic armies dragged European prisoners off to the markets of Algiers and Istanbul. They could be ransomed if their friends or relatives knew where to find them, otherwise they were never heard of again. The first Scottish philosopher to write on the subject of slavery, John Mair in the 16th century, quoted Aristotle with approval. Which makes it all the more remarkable that a later Scot, Adam Smith of Kirkcaldy, took a quite different line.

On the contrary, slaves were inefficient workers because they could have no personal interest in their work

Smith was not interested in aping Christian morality. He found it hypocritical. So what he did when there was some aspect of society he wanted to criticise was to look for practical examples and to see how he could apply to it his own liberal principles. In the case of slavery, he argued against it, not on the grounds it was morally offensive but that it was nowhere near as profitable as its commercial supporters claimed.

On the contrary, slaves were inefficient workers because they could have no personal interest in their work. That personal interest could only be created if they grew and harvested crops they had sown for themselves. A system of private property and free markets would be far better for everybody concerned than the system the UK had in its colonies, of enslaved workers and regulated markets.

In other words, a plurality of attitudes to slavery had developed just at the time, in the late 18th century, when the earlier acceptance of it was giving way to ethical rejection of it. Smith was widening the terms of argument to include those who believed slavery to be an economic necessity, whatever its moral status. He destroyed this argument and left the supporters of slavery with not a leg to stand on.

I’ve rehearsed this brief history of opinion about slavery in order to show it has never been uniform. Nor is it now, as in Scotland we join the global debate about whether we can in good conscience commemorate prominent figures from the past who have all the same countenanced a social institution so irrational and cruel. In our eagerness to prove ourselves worthy participants, however, we should also take care to keep clear heads and not bandy about our trendy opinions of dead men who have no chance to answer back.

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For example, Henry Dundas, political boss of Scotland in the late 18th century – and a friend and follower of Smith – did not favour slavery either. He was a practitioner of what the Scottish Enlightenment taught, and one theme of his career had been legal reforms to widen personal freedom.

NOW he spoke against the slave trade in the House of Commons, and never in the future contradicted himself. Those who want to topple his statue in St Andrew Square, Edinburgh, should first be required to quote from his copious writings and speeches a single sentence that shows support for the slave trade or slavery. They will fail because there is none.

Dundas lobbied and cajoled and wangled a majority of MPs on to his side. But his legislation was defeated when it went to the House of Lords

The whole present fury against him has arisen because of his role as chief man of business for the government of William Pitt the Younger in the 1790s. Pitt believed the slave trade should be ended by legislation, a point of view he had picked up from the leading abolitionist in the UK, William Wilberforce. But there was no majority for it in the House of Commons, dominated as this was by moneyed interests in the City of London, whose portfolios of investment often included slave plantations.

Amid the complexity the government, picked Dundas to set about finding a way through. This was a normal kind of business for him, cobbling together majorities for laws that would never be popular but might prove useful.

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Every successful political system needs people like Dundas, who rather than make long speeches on grand principles perform the hard graft and the dirty work inevitable in a parliamentary system.

The UK at the time was not a democracy, but it did have such a parliamentary system. Convictions and interests were in constant conflict and compromise, as they still are today. They did not make life easy, but put a stop to policy being dictated from on high.

In the event, Dundas never succeeded with the bill he brought forward in 1792. As ever he had been ready to do a deal, proposing, for example, that the abolition should be not immediate but gradual (in practical reality it could hardly be anything else). The eventual agreement was that the slave trade would have ended by 1800.

Dundas lobbied and cajoled and wangled a majority of MPs on to his side. But his legislation was defeated when it went to the House of Lords, where the pressure he might exert on the peers was far less. He could do no more. He accepted that result and dropped the whole matter.

It is bizarre for us in the modern UK to claim this process was anything but normal. Look at Brexit: how long did that take to get through? Look at deeper moral issues, the death penalty or abortion rules. Would anybody suggest that, because legislation did not succeed at the first attempt, then somehow its sponsors were its secret enemies?

Yet that is what we are asked to believe by Adam McVey, leader of Edinburgh council, and Geoffrey Palmer, former professor of brewing at Heriot-Watt University, these two being local leaders of a campaign against the memory of Dundas.

On the contrary, he should be honoured for the legislation which, though defeated in the short term, helped to create the conditions for the actual abolition of the slave trade in 1807, just 15 years later.