Things haven’t changed much in two thousand years. One might add that there is nothing so foolish that has been said by a philosopher that many people have not believed it.

These inspiring thoughts were provoked by reading a book, Practical Ethics, by one of the most famous philosophers of our time, Professor Peter Singer, now of Princeton University. Whether he is as eminent philosophically as he is famous I leave to philosophers to decide. But the great success of his books suggests that he has been influential: for example, Practical Ethics was reprinted nine times in the first four years after its publication.

Professor Singer writes clearly, so that his views are comprehensible to any normally intelligent person. And this is no small merit, given philosophers’ history of deliberate obfuscation, particularly of late, and particularly in the country where I write this, France.

But clarity has its drawbacks, at least from the point of view of th...