What are the true essentials of mysticism? When we have stripped off those features which some mystics accept and some reject—all that is merely due to tradition, temperament or unconscious allegorism—what do we find as the necessary and abiding character of all true mystical experience? This question is really worth asking. For some time much attention has been given to the historical side of mysticism, and some—much less—to its practice. But there has been no clear understanding of the difference between its substance and its accidents: between traditional forms and methods, and the eternal experience which they have mediated. In mystical literature words are frequently confused with things, and symbols with realities; so that much of this literature seems to the reader to refer to some self-consistent and exclusive dream-world, and not to the achievement of universal truth. Thus the strong need for re-statement which is being felt by institutional religion, the necessity of re-translating its truths into symbolism which modern men can understand and accept, applies with at least equal force to mysticism. It has become important to disentangle the facts from ancient formulæ used to express them. These formulæ have value, because they are genuine attempts to express truth; but they are not themselves that truth, and failure to recognize this distinction has caused a good deal of misunderstanding. Thus, on its philosophic and theological side, the mysticism of western Europe is tightly entwined with the patristic and mediæval presentation of Christianity; and this presentation, though full of noble poetry, is now difficult if not impossible to adjust to our conceptions of the Universe. Again, on its personal side mysticism is a department of psychology. Now psychology is changing under our eyes; already we see our mental life in a new perspective, tend to describe it under new forms. Our ways of describing and interpreting spiritual experience must change with the rest, if we are to keep in touch with reality; though the experience itself be unchanged.