‘If you are a citizen of the world, you are a citizen of nowhere,’ proclaimed Theresa May in a speech to the Conservative party conference. Oh dear! And her a vicar’s daughter too!

‘Cosmopolitan’ derives from the ancient Greek kosmos ‘world’ plus politês, ‘enfranchised member of a polis, citizen’. It was a word used by the 4th century BC philosopher Diogenes to describe himself when he was asked where he came from. Famous for living ‘like a dog’ (kunikos, whence ‘cynic’) and rejecting all conventional values, it seems that he was claiming to be an example of a man wholly in tune with nature and existing on a higher plane of virtue that should embrace the whole world.

Diogenes was taking to extremes an idea that Greeks had been debating for some time, that there were values that rose about local concerns and tied all humanity together. It was Roman Stoic thinkers who developed this debate in a world that was becoming increasingly ‘cosmopolitan’ in itself as the Roman Empire expanded from Britain in the west to Persia in the east and North Africa and Egypt in the south.

Taking ‘reason’ to be the divine (and therefore universal) element in man and ‘law’ its logical extrapolation, the Stoics thought of the whole kosmos as a form of polis, governed by divinely inspired law. The philosopher Philo (1st century AD) put it like this: ‘A man who is obedient to the law, being, by so doing, a citizen of the world, arranges his actions with reference to the intention of nature, in harmony with which the whole universal world is regulated.’ But that did not mean one rejected one’s own polis in favour of the greater one: far from it. It was one’s duty to serve humanity as best one could, whatever the arena, great or small.

This image was meat and drink to early Christians. Taking it to mean a religious community of all peoples, they envisioned a world joined as one, becoming through Christ ‘fellow citizens with the saints’. Unlike Mrs May.