We can say at once that considering the complexity and multiformity of psycho-physiological phenomena there would seem to be no _a priori_ reason why all subconscious phenomena must be the same in respect to being either coconscious or unconscious; some may be the one and some the other. It is plainly a matter of interpretation of the facts and there still exists some difference of opinion. The problem is a very difficult one to settle by methods at present available; yet it can only be settled by the same methods, in principle, that we depend upon to determine the reality of a personal consciousness in other persons than ourselves. No amount of _a priori_ argument will suffice. Perhaps some day a criterion of a conscious state of which the individual is unaware will be found, just as the psycho-galvanic phenomenon is possibly a criterion of an effective state. Any conclusions which we reach at present should be regarded as provisional.[79] SPECIAL PROBLEMS OF THE SUBCONSCIOUS As one of our foremost psychologists has said, the subconscious is not only the most important problem of psychology, it is _the_ problem. But of course it involves many problems of practical and theoretical interest. Among them are: First of all the evidential justification of the postulation of subconscious processes in general. Second; the intrinsic nature of such processes. In other words and more specifically, whether the neurograms of experiences after becoming active subconscious _processes_ continue to be devoid of consciousness, nothing but a brain process,—i.e., unconscious; or whether in becoming activated they become conscious (monism), or acquire conscious equivalents (parallelism), notwithstanding they are outside (dissociated from) the content of the personal consciousness. Third; the kind and complexity of functions a subconscious process can perform. Can it perform the same functions as are ordinarily performed by conscious _intelligence_ (as we commonly understand that term); that is to say memory, perception, reasoning, imagination, volition, affectivity, etc.? If so, to what extent? Fourth; are the processes of the conscious mind only a part of a larger mechanism of which a submerged part is a subconscious process? Fifth; to what extent can and do subconscious processes determine the processes of the conscious mind and bodily behavior in normal and abnormal conditions? These are some of the problems of the subconscious which for the most part have been only incompletely investigated. It is, of course, beyond the scope of these introductory lectures to discuss with any completeness the evidence at hand bearing upon these problems or to even touch upon many of the points involved. We may, however, study more deeply than we have done some of the phenomena with which we have become familiar with a view to seeing what light they throw upon some of these problems, particularly the first three.