How do you win an argument? Actually, forget an argument, how do you convince others to see your point of view and change their opinion?

Do you: (A), march around with a bunch of people who believe the same things you do? Or (B), engage with your opponents, listen, show respect, set out your position, and hope others come round to your way of thinking?

It’s never ceased to be a matter of fascination that much of the grassroots Yes movement finds itself incapable of working out that (B) is the answer. You don’t need to be Cicero to understand that looking outward, rather than inward, is the only way to get others to listen to your argument and shift their worldview.

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It’s a fundamental of rhetoric: you can’t debate in an empty room, unless you’ve a screw loose. So, Humza Yousaf is entirely right to turn down an invitation from All Under One Banner – the Yes group that marches around Scotland – to attend one of its rallies.

What’s the earthly point of a bunch of people who believe the same things telling each other they believe the same things? Well, let me correct myself. There is a point: the point is to reassure yourself that you’re right. The Yes movement – at least the AUOB iteration – seems so fragile it must be constantly on parade to convince itself God is on its side.

There’s an inherent risk here, of course. By parading around and telling yourself you’re right all the time, you repel those who don’t agree with you, and deter those who sit in the middle unconvinced.

A march with flags and slogans is tribal. It says "this is my group and you’re not in it". It doesn’t offer welcome, or invite others to listen. It’s us and them. By marching around with Saltires, groups like AUOB immediately "other" unionists and undecideds, when they should – at least one hopes – want to convince them of the merits of independence.

Not for the first time do the more febrile elements of the Yes movement bring Norman Mailer’s famous comment about America at the height of the War on Terror to mind. Mailer described the fragility of an all-powerful America as equivalent to mythical Adonis sniffing his own armpits every few minutes to reassure himself that he was still the most gorgeous man on Earth.

“What would we think,” Mailer asked, “of someone who was seven foot tall, weighed 350 pounds, was all muscle, and had to be reassured all the time? We’d say ‘that fella’s a mess’.” America had to learn to take criticism, acknowledge its mistakes, Mailer said. “It’s an obligation to improve all the time, not to stop and take bows and smell your armpits and say: ‘Ambrosia’!”

The Yes movement does a lot of armpit-sniffing. It should stop.

If Mr Yousaf attends an AUOB rally he’s saying two things: firstly, "I’m not interested in engaging with unionists and undecideds, I want to talk to my people, they’re all that matters". And secondly, he’s implicitly sneering at unionism, and rejecting – even denigrating – the views of roughly half the nation.

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If anyone thinks that’s the way to win independence, they need their head examined. AUOB is now furious with Mr Yousaf. He’s “reactionary and contemptuous” apparently. He displayed “de facto anti-Yes behaviour”.

Wrong. He made the right choice. The only "anti-Yes behaviour’ – though doesn’t that sound quite Maoist? – comes from those who wilfully fail to engage with unionists.

If the Yes movement wishes to advance, it should perhaps heed the trajectory of nationalism in Northern Ireland. There’s been a determined emphasis on listening to and respecting unionists of late. That’s clearly paid off. More and more young people – and some not so young – from a unionist background are beginning to embrace the notion of a United Ireland.

There will also be a senior SNP figure at the AUOB march, so the party can play both sides: keep throwing red meat to the base – a tactic of mere mollification rather than advancement – while not disrespecting unionists through the presence of the First Minister. Evidently, Yes voters can disrespect unionists if they wish – and many surely do – but they need to know that they slit the throat of independence through their behaviour.

What should be of greater concern to the Yes movement is that on the same day as the AUOB march, the SNP plans to hold an "independence convention" – open to party members only. So in this instance, the SNP has chosen to talk to itself, not to the people of Scotland, whether unionist, undecided or pro-Yes.

The "independence convention" which the Yes movement needs – which Scotland needs – is one that embraces the people, not the narrow interests of Yes-supporting political parties, be they SNP, Greens or Alba. The Yes movement will only move forward when ordinary non-partisan Scots feel they’re part of this conversation.

Why would someone who has rejected the SNP their entire life ever give a moment’s positive consideration to independence if the SNP is seen as the vehicle and mouthpiece? They might listen to academics, though. Trade unionists, church figures, folk from think-tanks, writers, actors, business men and women, charity workers, community activists, people who run food banks, poverty campaigners. Ordinary folk.

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The Yes movement needs to realise that when it comes to independence it is the least important part of the equation. It doesn’t matter if the Yes movement feels happy and loved. What matters is that unionists are embraced and can, if they chose, make the journey from No to Yes.

Clearly, the best way to make the case for independence is for the SNP to govern Scotland well. It’s that simple. Though we’ve seen damn little of that lately. By constantly putting the constitution first, the SNP has created its own gallows: American-style political polarisation which makes progress on policy impossible. Everything becomes a war because the SNP presents itself as a constitutional campaign rather than a vehicle for government policy. Just look at the ferocity conjured up by a deposit return scheme.

The success of independence depends on this: Mr Yousaf embracing the other 50% of Scotland, not his own side. The Yes movement must do the same.