Recent discussion has led to a recognition Christian mysticism differs fundamentally from that of the non-christian religions. It was necessary, first of all, in face of the historical positivists to show where this difference lies. The answers so far proposed indicate at least that this is to be sought in the trinitarian structure of our theism. It is remarkable how little this has been taken into account by the theologians of the last centuries, and how little influence it has had on Christian life. In theory the West has never lost sight of the unique nature of christian, i.e. trinitarian, theism, but in practice the Christian and non-Christian mystic differ less markedly. We do not account for this difference simply by saying that the revelation of the Trinity and the substitution of trinitarian forms for mono-theistic characterise Christian mysticism, for this would be to beg the question which is precisely how this reference to the Trinity makes Christian mysticism so unique a thing.