“DO I contradict myself? Very well then I contradict myself (I am large, I contain multitudes.)” Large though Walt Whitman may have been, however, he was a skelf compared with the megalo-colossal figure of Ian Blackford MP, who in the past couple of days has described the current situation as “a disaster”, “catastrophic”, an attempt “to shut down democracy” and “a fantastic opportunity”.

Whitman’s genius was, of course, to recognise that apparent opposites sometimes co-exist. And the SNP Commons leader’s endorsement of all those characterisations may seem to make sense, given that his natural position is to view anything that’s potentially difficult or disastrous for the UK as a potential boost for the cause of independence.

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Yet Mr Blackford, even as he no doubt contemplates Leaves of Grass’s declaration that “facts are useful, and yet they are not my dwelling” has a lot of contradictions to juggle. It may be consistent to use the fallout from ignoring a democratic referendum as a springboard to overturn the result of another democratic referendum. But the argument runs into trouble when you want to use it as a mechanism to implement a third referendum, to overturn both the others.

The SNP favours a general election because the party can expect to do well at it. Even if no election transpires, because of the vagaries of the Fixed Term Parliaments Act, the Nationalists are in a powerful position to back some alternative, such as a so-called Government of National Unity, however fanciful, incoherent or anti-democratic such a move might be.

Their strategic position is strong; it’s just that the justifications offered for it aren’t. On the face of it, there’s nothing odd about wanting both an independent Scotland, and wanting it to stay in the EU. But it’s coherent only in the abstract, paradoxical world of Whitman’s poetic transcendentalism. In the real world, it involves defining phrases like “political union”, “democratic mandate” and “national interest” differently almost every time you use them.

If the justification for blocking Brexit is that Scotland overwhelmingly voted against it in the EU referendum, you can’t paint an upcoming election as a mandate to ignore the equally clear result in the “once in a generation” independence one. And you especially can’t do it by arguing that the position has changed – because the way in which it has changed is that a vote to take us out of the UK would be a vote to take us out of the EU.

It’s a nuisance for Europhile Nationalists that the vote to reject independence meant that the majority Scottish opinion became a minority view across the UK electorate. But that’s democracy for you. The majority of Londoners are in the same boat (and, in any case, there’s a sizeable minority of Leave voters in both places).

Subsequent events have shown that the Nationalist claim that Scotland could have remained in the EU without reapplying, had we left the UK, were no more than wishful thinking – even if you don’t get into the arguments about whether an independent Scotland’s economy would meet the membership criteria, or how long it would take to get back in.

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If you take the position that Brexit is damaging, and opposed by majority Scottish opinion, it’s perverse in the extreme also to regard a vote for the SNP as an instruction to seek a second independence referendum that (if successful) would result in the same thing. Leave aside the fairly obvious point that one of the lessons of the Brexit process so far is the difficulty and dire economic ructions of getting out of a close political union. Scottish exit from the EU would immediately follow a pro-independence vote, whether or not the rUK had achieved Brexit in the meantime or not.

If the SNP fights an election on the principle that it can ignore the anti-democratic nature of opposing Brexit for the UK because there’s a Scottish mandate against it, it must logically accept that there’s also an instruction from the Scottish people to remain in the UK.

If it ignores the principle, and argues from the political practicality that people were misled about the difficulties, and may have changed their minds, it can either do so with reference to the electorate across the UK, or Scottish voters, but not both.

Any economic or political case against Brexit not only goes double for leaving the UK, but demands that the SNP either stays in the Union arguing against Brexit, or regards it as a justification for independence. As with the principle, a vote for the SNP can’t in practical terms be at once a vote to save the UK from Brexit, and to justify a second independence referendum. Not least because, if it were, it would guarantee Brexit on both sides of the border.

Whitman was able to declare himself “One of the Nation of many nations, the smallest the same and the largest the same”, but Mr Blackford can’t pick and choose. If the SNP isn’t honest about what a vote for them could deliver, and which option they would choose, it’s hard to see why they deserve support.