The claims of semantics can be illusory, threatening the innocent answer with unsuspected heredities. There is an ever-present gnosticism, heightened nowadays by the methods and vocabulary of psychology, which sees hidden depths of meaning in very ordinary shallows. Yet there can be no denying that discussion too often ends in futility because it has not been preceded by the definition of the terms to be used. This is one of the most frequent sources of disagreement, for instance, in international conferences: “ democracy”, “free elections”, “minorities”—unless there is an honest attempt at determining what the terms mean, subsequent disputes will derive from the varying interpretation, held doubtless in all good faith, of such concepts.In the theological sphere, careful definition of dogmatic truths is an essential prerequisite of their discussion. That is why so much zealous work for Christian reunion has achieved disappointing results : good will has been substituted for the often unpleasant task of establishing the basis of discussion. The result in the end is bound to be inconclusive, for the evasion of the primary meanings of the truths of faith must affect even the most neutral attempts at co-operation. It is true that united action on a specific moral issue need not demand an identity of belief in the Blessed Trinity among the participants. Yet in the long run, and inevitably, action can claim no autonomy from the demands of belief.