In 1966 Peter Stein, at that time Professor of Jurisprudence at the University of Aberdeen, published his excellent book Regulae Iuris, subtitled From Juristic Rules to Legal Maxims. While reading it again recently it occurred to me that a famous legal maxim was absent: the rule audi et alteram partem, sometimes also formulated in better Latin as audiatur et altera pars. Since the rule is of paramount importance to all who are, like myself, professionally concerned with a fair administration of justice, I think it right and proper to devote this contribution to it, as a rather late tribute to Peter Stein's work on the regulae iuris.

The principle audi et alteram partem, which, in the Common law, is regarded as one of the rules of natural justice, is not only self-evident but also – and perhaps for that very reason – valid for all time, as John Kelly showed some years ago.

Therefore, the fact that we can hardly find any text in the Corpus Iuris Civilis which explicitly refers to it should not lead us to the conclusion that the Romans did not recognise this principle. There is much evidence in sources outside the Corpus Iuris confirming that such a principle was held by philosophers and jurists, as Kelly has convincingly shown.