JK Rowling's 1500-word epistle on independence might be the best thing written in defence of a No vote.

The fact that it is more eloquent than anything else produced by Better Together is telling, but never mind. Rowling is honest, if wrong; thoughtful, if misinformed; generous, yet stranded in a world that is passing.

As a contribution to debate, the statement is exemplary, much like the response it has drawn from Mairi McFadyen of the National Collective group. Neither woman indulges in flyting in the old, tedious style. Neither forgets the word "respect". Reading their articles is like watching two people stare through the same window. One sees only massing clouds; the other sees light flooding the horizon.

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Not everyone gets the point of why civility matters in this argument, why content so often depends on manner. Some have no desire to get the point. No sooner does Rowling write that "there is a fringe of nationalists who like to demonise anyone who is not blindly and unquestionably pro-independence" than a handful of carefully- anonymous, semi-literate creeps duly oblige. Headlines follow.

Misogynists are the crawling vermin of the online world. Rowling does not say - for perhaps she doesn't know - that women who support Yes are also treated to the attentions of men who flush the contents of their minds over social media. The world of Twitter is ugly often enough; we can all show scars. But the treatment of women, all women, in language you won't see reproduced here, remains its hallmark.

Last week, ­crawling sorts treated Rowling abominably. To her credit, and unlike the political operators desperate to defame an entire movement, she had recognised a minority for what it was, writing that, in her belief, "intelligent, thoughtful people predominate" in the debate. The point is important. On September 19, when this is over, one large part of the Scottish electorate will have seen its wishes denied. The fact will have to be absorbed, the consequences accommodated.

Stick to arguments, then. ­Rowling says there are those who "try to make this debate about the purity of your lineage". That's not false: some, a few, do just that. But what is also true is that the vast majority recoil even from the word "purity", if they can make sense of it all. They hold to William ­McIlvanney's boast, years back, that we are a mongrel nation, defined only - as Rowling defines herself - by an ­allegiance "wholly to Scotland". Most are baffled to be insulted as "ethnic separatists".

Among other things, Rowling believes the Union saved Scotland from economic catastrophe when the banks tottered. She does not address the truth that Westminster, suborned by the City, allowed bankers to debauch the system and cause it to totter. Nor does she have anything to say about the insanity of the ensuing austerity that has become, for many Scots, the black joke of "better together".

The writer instead sticks with the Unionist idea that an independent Scotland would depend - for we are ever dependent - on North Sea revenues. The reality of GDP numbers says that oil and gas ought to be our bonus balls, not our national living wage. The quickening pace of exploration also demonstrates that the treasure will not be depleted for at least another generation. We would have to cope with "volatility" in prices? Sovereign countries do that kind of thing.

Though she treats optimism as a "romantic outlook", Rowling admits (with no little pride) that Scots have made many marks on the world thanks to remarkable people "in quantities you would expect from a far larger country". Some of us are so accustomed to the unromantic fact we take it for granted, but the writer who conjures magic worries over "the denial of risks". She means, I think, that no-one on the Yes side has come up with one of those infallible talismans against every possible future danger. So which UK politician has ever mastered that sorcery?

Europe, the currency, the ­economy: despite every description of what is most likely, on the dull grounds of common sense, ­Rowling prefers the Better Together tale of, say, thwarted EU membership. Rather that, it seems, than any ­fretting over what the Tories might do in 2017 to force Scotland out of the community. Harry Potter's creator also seems to believe that for a lot of us this plot is driven by a wish to "stick it to" a minor character named Cameron. In truth, the outcome falls into the necessary but not sufficient category.

Risk is the writer's theme. She associates it entirely with a belief in independence. Though the idea of opportunity is acknowledged, Rowling does not seem to believe there is any risk in voting No. The daily experience of Scots, the future promised by George Osborne and Ed Balls alike, says she is dead wrong. The biggest, wildest gamble on September 18 will come with a No vote, even - perhaps ­especially - for the medical research that is close to her heart. The international reputation of Scottish science is not a gift from Whitehall. It was earned here.

Rowling's final substantive point is to argue that Scotland will be popular as never before in ­Westminster if we choose to vote No. That's nice. What's more, we will be able to "dictate terms". Is that all the Union means? Must it amount to no more than demanding attention and issuing demands? That's not inspiring. In logic, it means, too, that when next the relationship is out of kilter we have to start all over again. "Give us more powers or else" is neither fit behaviour nor a formula for enduring harmony.

Predictably, Mairi McFadyen's glimpse through a streaked window makes more sense to this reader. Are there risks in a Yes vote? Of course. Would independence be easy? Of course not. Is the perpetual smiling optimism of the Yes campaign worthy of scepticism? People campaign as they must, given what is ranged against them, but it never hurts to be sceptical.

It doesn't hurt, either, to consider the essential nature of the Yes movement, as McFadyen urges. In her telling, the hope for an independent Scotland lies in the very character - in the youth, energy, inventiveness, optimism and desire - of the campaign.

Better Together has given up on that front. It devotes itself to wielding its media free pass and to the effort to portray good people as abusive racists. For negative campaigning never fails, so the thinking goes: that's rule one. To her eternal credit, JK Rowling, off-key just once or twice, refuses to be duped into playing a miserable game. A reasonable debate between reasonable people with only their country's interests at heart: who loses?

I could name a few who would feel deprived of their fun and their careers if that sort of thing caught on. There are others who delight in being nameless, others still who can only understand the pressing need for self-determination through the prism of what, sourly and cynically, they think they know about people. Never mind. When Scotland wins the chance to grow up, we can all grow up at last.