A second-hand bookshop in my high street said that it could not buy some old books from me, but that it would take them off my hands for nothing to stop me giving them to a nearby charity shop that is killing the bookseller's custom by being able to acquire books at no cost. What price on preserving the fast-fading commercial life of our high streets, versus the odd mosquito net here or there?

When choosing how best to improve the world, why make your choices so black and white? There is no league table of worthy causes (is it better to donate to a cancer charity than one alleviating suffering in Mali?). If there were, all charity would be funnelled towards only the one, “most deserving” recipient. Equally, why need one passion - preserving your high street, say, or wiping out malaria - dominate to the point of excluding all the other passions in your life? Mosquito nets certainly sound the more noble bet. But the bookseller also has a family to feed.

Why can you not split your generosity between bookshop and charity shop? You cannot berate others (or yourself) for choosing to help in this way, rather than in that one - just as you cannot chastise a generous philanthropist for not handing over even more of his billions to charity.

You can donate to charities that support cancer patients, while also helping those which bring clean water to Africa. So why can't you similarly aim both to preserve the vigour of your high street, while also helping your local charity shop? Both can, and should, survive. Indeed, if residents switch to nearby shopping malls because their high street has died, there would be no passers-by to pop into the charity shop anyway: so it is in the charity's interest, too, for the high street - and its second-hand bookshop - to flourish.