quickly’.19 It is certainly doubtful whether Cyril used it with the precision which came to be attached to it later. Wickham, for instance, translates kath’ hypostasin as ‘substantially’ in the passage from the Second Letter to Nestorius cited earlier, and this is justified to the extent that Cyril did not draw a sharp distinction between hypostasis and physis. If the union was one kath’ hypostasin it was also, as we have seen, one of mia physis. This interchangeability between hypostasis and physis