“It is not contrary to reason,” wrote David Hume, the 18th century Scottish philosopher, “for me to chuse my total ruin, to prevent the least uneasiness of an Indian or person wholly unknown to me.” The US, the UK, the EU and Nato have all said they will not directly intervene militarily to prevent the “uneasiness” of even some hundreds of thousands of Ukrainians (“Investigators start to gather evidence of possible atrocities against civilians”, Report, April 5).

But is there a threshold number for those suffering horrendous deaths — 5mn, 10mn or 20mn — which, if reached, leads the west to intervene, be it through reason, compassion or perceived self-interest?

And if that happens, what have we to say to those who were allowed to suffer and die before that threshold was reached?

Peter Cave
London W1, UK