The idea of a _threshold (limen, Schwelle)_, of consciousness;--of a level above which sensation or thought must rise before it can enter into our conscious life;--is a simple and familiar one. The word _subliminal_,--meaning "beneath that threshold,"--has already been used to define those sensations which are too feeble to be individually recognised. I propose to extend the meaning of the term, so as to make it cover _all_ that takes place beneath the ordinary threshold, or say, if preferred, outside the ordinary margin of consciousness;--not only those faint stimulations whose very faintness keeps them submerged, but much else which psychology as yet scarcely recognises; sensations, thoughts, emotions, which may be strong, definite, and independent, but which, by the original constitution of our being, seldom emerge into that _supraliminal_ current of consciousness which we habitually identify with _ourselves_. Perceiving (as this book will try to show) that these submerged thoughts and emotions possess the characteristics which we associate with conscious life, I feel bound to speak of a _subliminal_ or _ultra-marginal consciousness_,--a consciousness which we shall see, for instance, uttering or writing sentences quite as complex and coherent as the supraliminal consciousness could make them. Perceiving further that this conscious life beneath the threshhold or beyond the margin seems to be no discontinuous or intermittent thing; that not only are these isolated subliminal processes comparable with isolated supraliminal processes (as when a problem is solved by some unknown procedure in a dream), but that there also is a continuous subliminal chain of memory (or more chains than one) involving just that kind of individual and persistent revival of old impressions, and response to new ones, which we commonly call a Self,--I find it permissible and convenient to speak of subliminal Selves, or more briefly of a subliminal Self. I do not indeed by using this term assume that there are two correlative and parallel selves existing always within each of us. Rather I mean by the subliminal Self that part of the Self which is commonly subliminal; and I conceive that there may be,--not only _co-operations_ between these quasi-independent trains of thought,--but also upheavals and alternations of personality of many kinds, so that what was once below the surface may for a time, or permanently, rise above it. And I conceive also that no Self of which we can here have cognisance is in reality more than a fragment of a larger Self,--revealed in a fashion at once shifting and limited through an organism not so framed as to afford it full manifestation.