Over and over again in these lectures I have raised points and left them open and unfinished until we should have come to the subject of Mysticism. Some of you, I fear, may have smiled as you noted my reiterated postponements. But now the hour has come when mysticism must be faced in good earnest, and those broken threads wound up together. One may say truly, I think, that personal religious experience has its root and centre in mystical states of consciousness; so for us, who in these lectures are treating personal experience as the exclusive subject of our study, such states of consciousness ought to form the vital chapter from which the other chapters get their light. Whether my treatment of mystical states will shed more light or darkness, I do not know, for my own constitution shuts me out from their enjoyment almost entirely, and I can speak of them only at second hand. But though forced to look upon the subject so externally, I will be as objective and receptive as I can; and I think I shall at least succeed in convincing you of the reality of the states in question, and of the paramount importance of their function. First of all, then, I ask, What does the expression “mystical states of consciousness” mean? How do we part off mystical states from other states? The words “mysticism” and “mystical” are often used as terms of mere reproach, to throw at any opinion which we regard as vague and vast and sentimental, and without a base in either facts or logic. For some writers a “mystic” is any person who believes in thought‐transference, or spirit‐ return. Employed in this way the word has little value: there are too many less ambiguous synonyms. So, to keep it useful by restricting it, I will do what I did in the case of the word “religion,” and simply propose to you four marks which, when an experience has them, may justify us in calling it mystical for the purpose of the present lectures. In this way we shall save verbal disputation, and the recriminations that generally go therewith. 1. _Ineffability._—The handiest of the marks by which I classify a state of mind as mystical is negative. The subject of it immediately says that it defies expression, that no adequate report of its contents can be given in words. It follows from this that its quality must be directly experienced; it cannot be imparted or transferred to others. In this peculiarity mystical states are more like states of feeling than like states of intellect. No one can make clear to another who has never had a certain feeling, in what the quality or worth of it consists. One must have musical ears to know the value of a symphony; one must have been in love one’s self to understand a lover’s state of mind. Lacking the heart or ear, we cannot interpret the musician or the lover justly, and are even likely to consider him weak‐minded or absurd. The mystic finds that most of us accord to his experiences an equally incompetent treatment.