What appears to have been a chemical attack on the city of Douma in eastern Ghouta has drawn widespread international condemnation – and a denial of responsibility by the Syrian government. Similarly, the attempted assassination in Salisbury of the former intelligence officer Sergei Skripal and his daughter with the use of a nerve agent rapidly brought denunciation, and retaliatory action including the expulsion of Russian diplomats, from most Western governments.

Yet the war in Syria has been in progress for seven years and the latest estimates suggest that between 350,000 and half a million people have been killed, and millions more displaced. The footage from Douma undoubtedly shows bombing and widespread destruction, even if the latest deaths (at least 70 at the first estimate) were not caused by chlorine gas, as was suspected.

Nor is the murder of Vladimir Putin’s political opponents, including foreign citizens, politicians and journalists, new. Indeed, it is so depressingly common that it is implausible to the point of absurdity to think that such killings are not part of the Russian president’s modus operandi.

Of course both events receive attention, criticism and calls for action (even if none follows), but a particular, and almost universal, condemnation is forthcoming when chemical or biological weapons are employed. Why is their use – in fact, even their existence – thought so much worse than conventional weapons, when the conventional means of maiming, killing and destroying are often comparably horrific?

There are, I think, answers to this question that tell us something about the moral issues which arise when people, and nations, unleash unspeakable carnage and suffering on their fellow human beings.

An absolute pacificist position, such as that adopted by some Quaker conscientious objectors in World War II, naturally means that such questions would not arise. But whatever its merits, it is not widely shared.

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