I MIGHT have wondered whether history will describe the Shadow Chancellor John McDonnell as a “third-rate Poundland Lenin”, which is what Sir Nicholas Soames called him the other day, except that I’m pretty sure that history’s comment will be “Who?”

That’s not meant as a slur on Mr McDonnell, since it will be history’s judgment on almost everyone. Quick – who was Shadow Chancellor 20 years ago? If you replied Francis Maude, you’ll be a great asset in a pub quiz team, but you’re probably a bit of a weirdo. I can barely remember anything about Lord Maude, even though he was trade minister until a couple of years ago and I once sat next to him at dinner.

Most people, even those who once ran half the world, don’t get remembered much, or at all, and most of us don’t even know very much about the historical figures of whom we have managed to hear. And their fame hasn’t anything to do with merit; in fact, rather the opposite. After all, everyone’s heard of Hitler, and the consensus view is that he was (to use Sellar and Yeatman’s definition) a Bad Thing.

Which, in a roundabout way, is why Mr McDonnell was being criticised by Sir Nicholas, a grandson of Winston Churchill, who – having defeated Hitler – is thus reckoned a Good Thing. Mr McDonnell’s view, however, is that Churchill was more villain than hero.

He cited Tonypandy, where troops were mobilised against striking miners in 1910, while Churchill was Home Secretary. As it happens, there’s always been quite a lot of dispute about that incident, but we’ve also recently had the Green MSP Ross Greer describing Churchill as a “white supremacist” and “mass murderer”.

A lot of people who hold what must be the conventional view (that is, that Churchill was a great national hero) got very annoyed by these characterisations of the wartime leader. But, without going into the details of where Mr McDonnell and Mr Greer may be right or wrong, it’s not inconsistent to admire some qualities, such as defeating the Nazis, while deploring others, such as mass murder. I’m thinking, of course, not of Churchill but Stalin, who probably did even more to win the war, but was unquestionably a mass murderer and dictator himself.

And no matter how much you may admire Churchill, he certainly had views that would nowadays be tricky to defend. The normal response, to argue that one needs to see historical figures in the context of the accepted mores of the time, seems the commonsense one, but Churchill seems to have been obviously racist even by the standards of his own day.

Read more: McDonnell brands Churchill a villain

More interesting than the particular case of Churchill, though, is the degree to which it is possible to condemn or exculpate historical figures on the basis of contemporary beliefs at all. Modern liberal norms ultimately have their roots in the Enlightenment, when certain ideas – liberty, religious freedom, tolerance – were pronounced “self-evident”. But it’s not clear that they were, even to the man who wrote those words in the Declaration of Independence. It’s even harder for us to decide whether to praise Thomas Jefferson for having asserted that “all men are created equal”, or pronounce him a villain and a hypocrite (worst of all possible contemporary charges) because he owned slaves.

Then again, the men – when it comes to history, it’s almost always men – who campaigned to outlaw slavery would probably be regarded as extremely racist by today’s standards. To see how quickly attitudes can change, try reading Hansard’s accounts of the debates on liberalising the laws on homosexuality or abortion. Much of what was said then, by those who were arguing for reform, would now be characterised as outrageously bigoted.

The trouble is that post-Enlightenment thinking, because of its belief in rights and progress, cannot help but regard itself as morally superior to the past. It’s easy enough to assess whether we have made material progress in anything from dentistry to fuel efficiency, or average wages or life expectancy. (We have, lots.)

We can’t make the same judgment about moral improvement, even if we are convinced of the intrinsic value of ideas like equality before the law, democracy, or the separation of church and state. It’s quite likely that in 50 years’ time – as with those debates in the 1960s – the future’s view of some opinion that is almost universally held now will be that it was bigoted and obviously wrong.

Assuming our moral superiority also makes it difficult for us properly to assess, and thus learn something from, the past. It’s not just that some current views (say, on sexual identity and behaviour) would be regarded as wicked by, for example, the Victorians. It’s that for, to take a different example, the ancient Greeks, they would be incomprehensible.

Yet the Greeks grappled with – invented the idea of grappling with – many of the foundational questions of morality still being debated. There’s a school of thought, albeit a minority one, which holds that they came up with rather better answers than we do.

The past, as LP Hartley famously put it in a book set in 1900, is a foreign country. But then Hartley mostly lived abroad, and didn’t much rate the present; he deplored what he saw as the vulgarity and immorality of his own era (1895-1972). Being a novelist, however, he was able to imagine it; which may be all we can do. We cannot see the past; we can see only the evidence it has left.

That’s why history is dominated by such regrettable things (to the modern sensibility) as kings, popes, and rich dead white dudes. It’s about the winners, the famous and the powerful, because they are the ones who got to write things down. And we are dependent on their opinions for our knowledge of their ancestors: if the Victorians had a distorted view of the Greeks, it can’t help but distort our view of both the Victorians and the Greeks.

Perhaps the most consoling statement on whether historical people were heroes or villains, or just rather like us, is the one produced by another novelist, in the great final sentence of Middlemarch, when George Eliot tells us that “the growing good of the world is partly dependent on unhistoric acts” and those who “lived faithfully a hidden life, and rest in unvisited tombs”.