It is used in a wider, looser sense and a narrower, stricter sense, which two senses are often confused in a way very detrimental to clear thinking. In the stricter usage the phrase implies the peculiar conception of human personality expounded at great length and with a wealth of learning and eloquence by Myers; it stands for an hypothesis which seemed to its author to bring almost all the strange facts he and his associates observed, as well as many alleged facts whose reality still remains in dispute, under one scheme of explanation and to bring them also into intelligible relation with the body of generally accepted scientific principles.
But the phrase "Subliminal Self" is now often used by those who do not fully accept Myers's hypothesis, as a convenient heading to which to refer all the facts of many different kinds that seem to imply subconscious or unconscious mental operations. This article is only concerned to expound the meaning of the phrase as it was employed by Myers, and it is much to be wished that it should only be used in this stricter sense. In the speculations of Schopenhauer and of Eduard Von Hartmann, the "Unconscious played a great part as: a metaphysical principle explanatory of the phenomena of the life and mind of both men and animals. But with these exceptions, the philosophers and psychologists of the 19th century showed themselves in the main reluctant to admit the propriety of any conception of unconscious or subconscious mental states or operations. The predominant tendency was to regard as the issue of "automatic" nervous action or of "unconscious cerebration" whatever bodily movements seemed to take place independently of the consciousness and volition of the subject, even if those movements seemed to be of an intelligent and purposeful character.
This attitude towards the subconscious is still maintained by some of the more strictly orthodox scientists; but it is now very widely accepted that we must recognize in some sense the reality of subconsciousness or of subliminal psychical process. The conception of a limen (threshold) of consciousness, separating subconscious or subliminal psychical process from supraliminal or conscious psychical process, figured prominently in the works of GT Fechner, the father of psycho-physics, and by him was made widely familiar. Fechner sought to prove that a sensory stimulus too feeble to affect consciousness produces nevertheless a psychical effect which remains below the threshold of consciousness, and he tried to show ground for believing in the existence of a vast realm of such subliminal psychical processes. But his arguments, founded though they were on epoch-making experiments, have failed to carry conviction; and it is in the main on other ground's than those adduced by Fechner that the reality of modes of mental operation which may properly be called subconscious or subliminal is now generally admitted.
During the last quarter of the 19th and the opening years of the 20th century, there had been accumulated a mass of observations which sufficed, in the opinion of many of those best qualified to judge, to establish the reality of processes which express themselves in purposeful actions and which bear all the marks from which we are accustomed to infer conscious cognition and volition, but of which nevertheless the subject or normal personality has no knowledge or awareness other than such as may be shared by any second person observing his actions. Among the commonest and most striking of such manifestations is the "automatic writing" which a considerable proportion of normal persons are capable of producing. A person who has this power may sit absorbed in reading or in conversation, while his hand produces written words or sentences, of which he knows nothing until he afterwards reads them. The matter so written varies in different cases from illegibly scrawled fragments of words and sentences to long, connected, sometimes eloquent, frequently more or less dramatic, disquisitions. In some cases the "automatically" writing hand can be induced to make intelligible replies to questions whispered or otherwise put to the subject in such a way as not to draw his attention from some other object or topic with which it seems to be fully occupied. In some cases the matter so written states facts previously known to the subject but which he is unable to recollect by any voluntary effort.
And in rare cases the matter written seems to imply knowledge or capacities which the subject was not believed to possess either by himself or by his friends. Other actions, including connected speech, may be produced in a similar fashion, and in the last case the subject hears and understands the words uttered from his own mouth in the same way only as those from the mouth of another person. "Table-tilting," "planchette-writing," and the various similar modes of spelling out by the aid of a code intelligible replies to questions, which have long been current in spiritistic circles and which, by those who practise them, are often regarded as the operations of disembodied intelligences, seem to belong to the same class of process. In extreme cases the manifestations of such subconscious or (better) co-conscious operations are so frequent, exhibit so much continuity and express so clearly a train of thought, purpose and memory, that they compel us to infer an organized personality of which they are the expression; such are the cases of double or multiple consciousness or personality. Very similar manifestations of a "co-consciousness" may be produced in a considerable proportion of apparently normal persons by means of post-hypnotic suggestion; as when suggestions are made during hypnosis, which afterwards the subject carries out without being aware of the actions, or of the signals in response to which he acts, and without any awareness or remembrance of the nature of the suggestions made to him. The more sober-minded of the investigators of these phenomena have sought to display all such cases as instances of division of the normal personality, and as explicable by the principle of cerebral dissociation (see hypnotism); the more adventurous, concentrating their attention on the more extreme instances, regard all such manifestations as instances of the possession and control (partial or complete) of the organism of one person by the spirit or soul of another, generally a deceased person.
Myers's hypothesis of the subliminal self was a brilliant attempt to follow a middle way in the explanation of these strange cases, to reconcile the two kinds of explanation with one another, and at the same time to bring into line with these other alleged facts of perplexing character, especially veridical hallucinations, various types of communication at a distance (see telepathy), and all the more striking instances of the operation of suggestion and of hypnosis, including the exaltation of the powers of the senses, of the memory and of control over the organic processes. Myers conceived the soul of man as capable of existing independently of the body in some super-terrestrial or extraterrene realm. He regarded our normal mental life as only a very partial expression of the capacities of the soul, so muchonly as can manifest itself through the human brain. He regarded the brain as still at a comparatively early stage of its evolution as an instrument through which the soul operates in the material world. So much of the life of the soul as fails to find expression in our conscious and organic life through its interactions with this very inadequate material mechanism re-mains beneath the threshold of consciousness and is said to constitute the subliminal self. The subliminal self as thus conceived would be better described as the subliminal part of the self, a part which surpasses the supraliminal or normal conscious self to an indefinitely great degree as regards its range of psychical faculties.
It was further conceived as being in touch with a realm of psychical forces from which it is able to draw supplies of energy which it infuses into the organism, normally in limited quantities, but, in exceptionally favourable circumstances, in great floods, which for the time being raise the mental operations and the powers of the mind over the body to an abnormally high level. It is a leading feature of,this protean conception, that many of the abnormal mental manifestations that have commonly been regarded as symptoms of mental or nervous disease or degeneration are by its aid brought into line with mental processes that are by common consent of an unusually high type, the intuitions of genius, the outbursts of inspired poesy, the emotional fervour or the ecstasy that carries the martyr triumphantly through the severest trials, the enthusiasm that enables the human organism to carry through incredible labours. Myers's hypothesis thus boldly inverts the dominant view, which sees in all departures from the normal symptoms of weakness and degeneracy and which seeks to bring genius and ecstasy down to the level of madness and hysteria; the hypothesis of the subliminal self seeks to level up, rather than to level down, and to display many of these departures from normal mental life as being of the same nature as the operations of genius, as being, in common with these, uprushes of the subliminal self, which temporarily acquires a more complete control of the organism and therefore achieves at such times a more complete expression of its powers. And these rare displays of subliminal capacities are held to foreshadow the further course of mental evolution, to afford us a glimpse of the higher plane on which the mind of man may habitually and normally live, if further evolution of the nervous system shall render it a less inadequate medium for the exercise of the spiritual faculties and for the influx of the psychical energies which at present, owing to its imperfections, are for the most part latent or confined to the subliminal self.
This bold and far-reaching hypothesis has not up to the present time been accepted by any considerable number of professional psychologists, though its author's great literary power has secured for him a respectful hearing. The comparative indifference shown to it by the scientific and philosophical world must be ascribed to considerations of two kinds. In the first place, it is rightly felt that a very large proportion of the alleged facts which it is designed to explain are not yet supported by evidence of such a nature as warrants an unreserved acceptance of them. Secondly, even if further investigations of the type of those carried on by the Society for Psychical Research should prove Myers's belief in the reality of all or most of these facts to have been well-founded, there will remain difficulties and weaknesses intrinsic to the hypothesis, which at present seem very serious. In addition to all the great difficulties that must attach to any conception of human personality as a spiritual entity capable of existing independently, of the body, Myers's conception raises many difficulties peculiar to itself, the chief of which may be briefly indicated. First, the conception of the relation of the subliminal to the normal or supraliminal self is in Myers's presentation extremely vacillating and uncertain, and it is probably radically incapable of definition and consistency. Secondly, two alleged supernormal phenomena, to the establishment of which "psychical research" has been devoted most energetically and (in the view of many of the workers) with the greatest success, and which from every point of view are the most important and interesting, are supernormal communications between the living (telepathy) and communication between the dead and the living. Now, if either or both of these modes of communication should eventually prove to be facts of nature, neither will need the hypothesis of the subliminal self for its explanation.
Such evidence as we have,of the latter kind of communication is almost wholly of the form of messages written or spoken by entranced persons which claim to be sent by the souls of the dead to friends still living, and these messages (if they are what they claim to be) imply, and were held by Myers himself to imply, possession or control of the brain of the living medium by the soul of the dead who transmits the message. Both phenomena need, then, for their explanation only the two great assumptions--first, that the soul is an entity capable of disembodied existence; second, that in its psycho-physical interactions any soul is not strictly confined to interaction with one particular brain. The third great difficulty is of an emotional order. All the laborious research whose results Myers has sought to harmonize by means of his conception of the "subliminal self" has been initiated and sustained by the desire of proving the continued existence of the human personality after the death of the body. But, if Myers's doctrine is true, that which survives the death of the body is not the normal self-conscious personality of a man such as is known and valued by his friends, but a personality of which this normal personality is but a stunted distorted fragment; and it would therefore seem that according to this doctrine death must involve so great a transformation that such slight continuity as obtains must be insufficient to yield the emotional satisfaction demanded. The hypothesis would thus seem to destroy in great measure the value of the belief which it seeks to justify and establish.
See also many papers by various hands in Proceedings of the Society for Psychical Research, especially in part xlvi., vol. xviii.