William and Kate: Romance and the Royals/Channel 4<br />Petworth House: the Big Clean/BBC4

It's still little reported in this country, but we are living through a revolution in the social sciences that will change politics permanently, mainly by exposing the binary distinction between Left and Right as immature gibberish. This research may have filtered through to you via Malcolm Gladwell's articles for The New Yorker; or in surveys of books with catchy titles like Nudge, Influence, Connected, and Predictably Irrational. The best yet is David Brooks's seminal The Social Animal, which documents new findings in fields as diverse as neuroscience and behavioural economics, and reports on their impact on social science.

A central insight of this "new humanism", as Brooks calls it, is that "emotion is not opposed to reason; our emotions assign values to things and are the basis of reason". Since at least Thomas Hobbes's day, we have considered reason and emotion as separate domains: head and heart, if you like. In fact, reason rides the emotions like a jockey atop a horse. The beast has the vigour; the rider gives it direction.

The ongoing failure of republicanism in Britain – despite the abdication crisis, the divorces of the 1990s, and Prince Charles's befriending of plants – has generally been interpreted as a microcosm of this crumbling dichotomy. The republicans' case owes everything to reasoned argument, such as the brilliant polemic by Johann Hari in these pages last week, or the writings of Toms Paine and Jefferson. The royalists' case owes everything to emotion, to the enduring affection we have for a national institution. The head says no, but the heart says yes. The heart wins.

David Starkey owes his on-screen career to adapting Brooks's insight for television. His whole persona barks at the screen: "You reckon this kings and queens lark is soppy and emotional? It's not, damn you! Think about it!" Last night he explicitly invited us to engage with an argument. He injected reason into all the chatter about this week's nuptials, which is drowning in emotion.

What was that argument? That Kate Middleton being a commoner is no great shakes. Starkey indulged the academics' favourite pastime in placing modern events in a much deeper context, in showing Middleton the commoner has predecessors. "Far from being a break with tradition," Starkey argued, "this is a return to it." He went on: "Aren't lineage and ancestry the true markers of class? Answer: they are not – and nor have they been for 700 years." Upon which our presenter mobilised a series of historical analogies. Katherine Swynford's "extraordinary liaison" with John of Gaunt circa 1370 opened the possibility that romantic love or erotic desire could influence a monarch's marriage. Swynford's sister was married to the poet Geoffrey Chaucer; ergo the Swynford sisters used marriage as a form of social climbing, just like commoner Kate. Elizabeth Woodville became the first commoner to marry an English sovereign (Edward IV, circa 1464). And who could forget commoner Anne Boleyn? "William and Kate, Henry VIII and Anne," Starkey said, "in both cases shared educational experience brings them together from different worlds."

How does Starkey's argument score? A solid B+. Kate has precedents. An interesting point, well made. But then this show veered off into the most bizarre conclusion. Even Starkey – Starkey! – couldn't resist the allure of emotional nonsense. Kate and Wills are now "the latest stars in the great international circus of celebrity," he said. "Helped by Kate, he shows signs of having learned he must do things a bit differently. The question is, have we? Maybe, if we and our media keep out of their way, this will be a royal love story where they really do live happily ever after. They deserve to."

Dear, dear, dear, Dr Starkey. What signs does he show? How was he helped by Kate? "Have we" done what, exactly? Do you really think our media will keep out of their way? Is that what this show is doing? Suddenly, a tight and interesting argument has been reduced to platitudinous drivel. We expect better from Starkey. For all that Brooks reports emotion and reason are intertwined, it seems our coverage of the monarchy is destined to elevate the former and relegate the latter.

And the deeper problem here is that Starkey's argument about Kate's commoner-ancestry is predicated on the idea that her lower station in life can help sustain public affection for the monarchy. But there is no evidence for this. For all that it is stuffed with propagandists, the scrutiny of the modern media can only continue to expose our royals for the mostly inoffensive toffs they are. And when the magic and pageantry fades, as it will from Saturday morning, what will be left?

Places like Petworth House, mostly. Designed by Capability Brown in the late 17th century, this mansion was undergoing, Andrew Graham-Dixon told us, "possibly the biggest spring clean in the world". I hate to be a bore, but that's just silly. What came across was the devotion of staff to finessing this stately home, now open to the public through the benefaction of the National Trust.

Graham-Dixon was a marvellous sport, getting stuck in as trees were felled across vast lakes. And just as members of a congregation know every last hidden detail of the church that unites them in piety, so the spring cleaners here felt an affecting sense of privilege at their access to the artefacts of the aristocracy. So long as they subscribe to the absurd myth that the inheritance of wealth gives these people moral and cultural authority, I kept thinking, Petworth House is safe. There's hope for Kate and Wills – and Starkey – yet.

a.rajan@independent.co.uk; twitter.com/amolrajan