The candidates battling for the leadership of the Labour party never stop banging on about ‘social justice’ and ‘equality’. But they never define them. Plato did. In his final work, Laws (c. 350 bc), three men, led by the unnamed ‘Athenian’, discussed general principles behind governance and the law. The Athenian then applied them to the proposed new Cretan city of Magnesia.

Plato defined ‘equality’ as (i) numerical or (ii) proportionate. This gave people what they merited, resulting in justice. So in Magnesia, private land-holdings were abolished and under (i), each household was given exactly the same amount of inalienable, heritable land, whose produce would serve the whole state. But, inevitably, some citizens would arrive with more wealth than others. So divide them into four property classes, and legislate that anyone coming to own more than a certain ratio of their land’s value would hand the surplus to the state. Result: no one would become very rich, because such people were not good and therefore not happy. To this end, gold and silver and lending at interest were forbidden, and coinage was legal tender among citizens, but valueless outside Magnesia.

Plato agreed that (ii) was a rough and ready calculation, but since no one was perfectly equal to anyone else (‘society consists of “unequals”’), the state would confer ‘high recognition on great virtue and treat others less well-educated in this respect as they merited’. Plato then outlined laws covering every aspect of life, and drummed in the central importance of the rule of law, to which everyone ‘must be a slave’. Since there was no greater virtue than obeying the law, those chosen for highest office were those best educated and therefore most obedient to it, and so on down the hierarchy.

As a result of Stoic and early Christian thought, the classical principle of a hierarchy of justice based on what everyone merited has been replaced in the West by the moral principle of respect for, and the equal worth and dignity of, all humans. But, as with Plato, that does not mean everyone is identical or must be treated uniformly — or does it, Sir Keir, Becky, et al?