Over the last two days there has been much singing of the Marseillaise.
It is a unique national anthem because, long before Friday's tragic events in Paris, it belonged to much more than its native country. It was composed as newly revolutionary France was menaced on all sides by the Armies of reaction and lost its original, rather literal, title, War song for the Army of the Rhine, in favour of its now much more famous appellation, when it was sung in the streets of Paris by volunteers (volunteers!) arriving there from the port of Marseille in 1792 to defend the revolution.
It was banned outright on the Bourbon restoration but whenever 19th century insurrection was in the air, initially in France, but later much widely across Europe, it became a rallying song of the forces of progress. It was even played at the Finland Station when Lenin arrived home there to herald the October Revolution.
But it also became something more. A musical shorthand for the aims of the (first) French Revolution; of liberty, egality and fraternity.
Its most famous cinematic rendition is in of course in the 1942 film, Casablanca. When Victor Laszlo instructs the band it be played to drown out the carousing Germans, it is both insignificant and very significant that Laszlo isn't himself French and it is not just the patrons of Rick's Café but cinemagoers the world over who find themselves metaphorically rising to their feet. Roy Hattersley once wrote of being strangely moved to tears by a National Anthem that is not one's own. Except that it is our own. It belongs to all of us. All of us who embrace the values of the enlightenment.
But the Marseillaise is something more as well. It is a war song.
It's final lines are these:
Aux armes, citoyens!
Formez vos bataillons!
Qu'un sang impur
Abreuve nos sillons!
For sometimes it is not just necessary to sing about your values. Sometimes you have to be prepared to fight for them.
And this I suspect may prove to be a matter of great significance for the internal politics of the Labour Party.
On the 12th of September 2001, in the NATO Council resolved that "if it is determined that the [Twin Towers] attack against the United States was directed from abroad, it shall be regarded as an action covered by Article 5 of the Washington [NATO] Treaty".
It was ultimately so determined and as a result NATO as a whole took action against Afghanistan.
That action might have been led by the United States but it was the treaty obligation of all NATO member states to assist the "member state" so attacked. As the United Kingdom did.
But there was another, very much minority, view at the time. That there was no reason or at least purpose to an attack on Afghanistan. That, in any event, to some degree or another, the United States had brought this assault on itself.
This body of opinion coalesced around the Stop the War coalition. It was that war, not the later Iraq War which brought it to much greater prominence, that is referred to in the organisation's title.
And there was at least a logical conclusion to the organisation's position. A conclusion that the UK should abrogate its NATO treaty obligations and, by implication at least, leave its framework of collective security altogether.
Now, at the time, this organisation had as one of its immediate leading lights, indeed later as its Chairperson, one Jeremy Corbyn MP. Within nine days of September the 11th he had declared himself opposed to any retaliatory military action whatsoever. And he remained thereafter consistent. As recently as September 3rd 2015, asked at the final Labour leadership debate if he could see any circumstance in which he would support the deployment of British troops abroad he replied that, while he was sure there were some, he couldn't think of any for the moment.
Well, that might have been a hypothetical question but this is not.
One of our oldest allies has been attacked. The home of the enlightenment, with, although this should be no more than incidental, one of the few socialist governments in Europe.. Attacked by people whose motivation appears to have been in part disgust at liberated women and whose specific targets at the Bataclan Theatre appeared to be particularly the disabled patrons in attendance. Attacked without warning and in the minds of almost all people of liberal opinion, without reason. In any sense of the word reason.
It appears Article 5 of the NATO treaty is again to be invoked and that, further to that, France is likely to take direct retaliatory military action against the places from which this outrage was planned. Action which we are treaty bound to assist.
So, Jeremy, is this finally a circumstance in which you will support the deployment of British troops abroad?
I suspect on the answer to that question will depend either the future of Jeremy Corbyn as leader of the Labour Party. Or, alternatively, the future of the Labour Party itself.