One very important question to be considered in all such investigations is, Whether our experience does not teach us that we are mentally so constituted that certain conceptions are necessary to us? Our mental nature is placed under certain laws, as our physical or corporeal nature is placed under certain other laws. One of these necessary conceptions, which are imposed on us, as it seems to me, by a law of our mental constitution, is a conception of the fundamental difference between matter and spirit. In what way is it forced upon us that there is a natural world and a spiritual world? The phenomena of matter and the phenomena of mind are essentially different. In ourselves they occur in conjunction, and they occur in disjunction. They are manifested synchronously, and they are manifested separately in point of time. The normal action of all the functions of the body is not necessary to the action of the mind. The body may be prostrated by disease, and the moment of its death may be at hand; yet the mind, to the last moment of the physical life, may be unclouded, and its manifestations may be as perfect as they ever were in the full health and activity of the vital functions of the body. No one who stands at a death-bed where this phenomenon occurs, and observes how completely the mind is master of itself; how it holds in consciousness the past and the present; how it essays to grasp the future for those whom it is to leave and for itself, can easily escape the conviction that death is nothing but the dissolution of the bond which has hitherto held together the two existences that constituted the human being, one of which is to be dissolved into its elemental and material substances, and the other of which is to go elsewhere, intact and indestructible.

Let me now refer to what is taking place while I am writing this essay. I have said that the phenomena of our bodily organism and the phenomena of our mental organism may occur synchronously in the same individual. The act of writing an original composition is an instance of this. The action of certain organs of the body and the action of the mind are simultaneous. In time, they can not be separated. In themselves, they are separable and separate. The thought springing up in the mind may be retained there, or may flow into language and be written by the hand upon the page. No one can detect in himself any instant of time when the mental formation of a sentence, or any clause of a sentence, as he writes, is separable from the physical act of writing. In that not very common, but still possible, feat of dictating to two amanuenses, at what appears to be the same time, on two distinct subjects, there is undoubtedly an appreciable interval, in which the mind passes from one subject to the other, and then back again, with great rapidity. But, when one is one's own amanuensis, when the act of thinking and formulating the thought, and the act of writing it down in words, is performed by the same person, there is a simultaneous action of that which originates the thought and clothes it in words, and the act of the bodily organ which inscribes the words upon paper. How is this phenomenon to be explained? And to what does it lead? Is there anything in the whole range of Mr. Spencer's "Psychology" that will interpret this familiar experience? May it not be interpreted by an anatomical examination of the mind as an organism?

I do not now refer to cases where a thought is completely formulated before the pen begins to be moved over the paper, and is then recalled by an effort of the memory and written down. I am referring to what I suppose is the habit of many persons in writing, namely, the origination and formulation of the thought as the hand moves the pen, a habit of which most practiced writers are perfectly conscious. The same thing occurs in what is truly called extemporaneous speaking,[142] when oral discourse is not a mere repetition, memoriter, of thoughts and sentences which had been previously formulated, but, as the word extemporaneous implies, when the thought and the language flow from the vocal organs eo instanti with their conception. In these and the similar cases of improvisation and animated conversation, in which there is a synchronous action of the mind and the bodily organs, it would be impossible for us to have that action if mind were constituted as Mr. Spencer supposes it to be. If there were no mind in the sense of an organized entity, conceiving a thought and clothing it in the language needful to give it written or oral expression, "if the ego were nothing more than the passing group of feelings and ideas"—if an "idea lasts (only) while the nerves of molecular motion last, ceasing when they cease"—if that which remains is (only) the "set of plexuses"—how could we originate any new thought? The very illustration to which Mr. Spencer resorts, when he likens the automatic human being to the non-automatic piano, and makes them analogous in their action, in order to show that passing ideas do not have a continual existence in the mind, but that the actual existence is the physical structure which, under like conditions, again evolves like combinations, reduces us at once to the level of the piano, and precludes the potentiality of a new and original idea which is not a combination of former ideas, and is produced under different conditions. The assertion or argument that each set of plexuses is capable of entering into countless combinations with others, and so renders possible future ideas, does not advance us one step to the solution of what takes place when we conceive a new thought, clothe it in language, and write it down on paper, or give it oral expression.

In justification of this criticism, let me now refer to that intellectual process which is called "invention," in its application to the mechanic arts. I do not mean to suggest or to claim that this kind of invention is an act which is to be referred to a distinct and peculiar faculty of certain minds, in the possession of which one man may differ from another. But I shall endeavor to describe what takes place when one conceives the intellectual plan of a certain new combination of mechanical devices, and embodies that plan in a machine which differs from all other previous machines in its characteristic method of operation. For convenience, I shall speak of the person who produces such a machine as the inventor, which is the same as speaking of him as the maker, as the poet is the maker of a poem. This act of invention, or the making of some concrete new thing, is an act of creation. The inventor, then, may be supposed to have learned all that empirical and all that scientific mechanics could teach him; to have had any quantity of passing groups of ideas pass through his consciousness; to be possessed of any number of plexuses capable of entering into countless combinations with others. These plexuses, or networks of transitory ideas, consisting of former impressions in the nerve-center, must, it is said, be recalled under the like conditions which produced them. But the conditions for the inventor are not the same. Something is to be produced into which the old ideas do not enter. There is to be a new arrangement of old mechanical devices; a new combination is to be made, which will possess a method of operation and accomplish a result never before seen or obtained. A new concrete thing, a new machine, is to be created. That the conception must be formed, that the objective point, to which the whole intellectual effort is to aim, must be seen, is manifest. A tentative intellectual process may have to be gone through before the full conception is reached, just as a tentative experimental process may be necessary in finding out how the practical embodiment of the conception is to be reached in building the structure. These processes may go on simultaneously or separately; but, when they are both completed, when the new machine stands before us, we see at once that the plan is an intellectual conception, perfectly original, and the physical structure is a new arrangement of matter effected by the hand of the inventor or by the hands of others, which he uses as his instruments in doing the physical work. I do not know, therefore, how this phenomenon is to be explained upon the theory that the only ego is the body and its functions, which lies behind and determines ever-changing states of consciousness. I know not how else to interpret the phenomenon of invention, excepting to adopt the postulate that there is a mind, a substantive existence, which, while its consciousness holds ideas suggested by former conditions, has the inherent power to originate ideas that did not form a part of any previous state of consciousness.

I have spoken of mind as an organism and as a substantive existence. This is a deduction to be drawn from the manifestations of mental phenomena. In order to guard against an objection that may possibly be interposed in the way of this method of investigation, I will anticipate and answer it. It will be said that we can not define or describe the substance of mind; can not tell whether it is a unit, in itself, or an aggregate of units; we know and can know nothing more than its approximate components, and all that we know of these does not justify us in assuming to speak of the substance of mind. I have more than once suggested, in our former conferences, that our inability to define and to describe the substance of any supposed existence is no proper objection to the hypothesis that there is such an existence. When we undertake to define matter, or to describe the substance of that which we call matter, we find that we soon reach a point where precise definition or description ceases. Yet we do not for that reason refrain from deducing the existence of matter from the manifestations of certain phenomena and from our experience with them. It is perfectly true that we know matter only by the manifestations of certain physical phenomena; that we can not define the nature of its substance. All we can do, by the most minute analysis, is to arrive at the perception of the ultimate particles or units of matter; and the nature of the substance of which these units are composed is incapable of any further description. "Matter"[143] is one of the words in the English language which are used in a great variety of senses, exact and inexact, literal and figurative. In its philosophical sense, meaning the substance of which all physical bodies are composed, the efforts of lexicographers to give a definition, descriptive of the nature of what is defined, show that definition is, strictly speaking, impossible. All that can be said is that matter is "substance extended"; or that which is visible or tangible, as "earth, wood, stone, air, vapor, water"; or "the substance of which all bodies are composed." But these efforts at definition express only what is needful to be expressed in contrasting matter with that other existence which is called "spirit." This is another word which is used in very different senses, but of which no more exact definition can be given, when it is used in its philosophical sense, than can be given of "matter." Lexicographers have defined "spirit," in one of its meanings, as "the soul of man; the intelligent, immaterial, and immortal part of human beings"; and in another of its meanings, more broadly, as "an immaterial, intelligent substance." In these definitions they have followed the metaphysicians, and the uses of the word in the English translation of the Bible. When we turn to the definition of "soul," we find it given as "the spiritual and immortal substance in man, which distinguishes him from brutes; that part of man which enables him to think and reason, and which renders him a subject of moral government." We also have it defined as "the understanding, the intellectual principle." Undoubtedly these definitions involve certain assumptions, such as the existence of a substance called spirit, and the existence of an intellectual principle, of which "soul," "spirit," and "intellect" are mere names. But there is no difficulty in the way of our knowing what is meant when these terms are used. The difficulty of giving a definition without a circuitous use of terms, explaining the one by the other, and then explaining the last by the first, does not prevent us from having a definite conception of the thing spoken of. When we speak of mind, soul, or intellect, what we think of is the something in ourselves of which we are conscious, and whose manifestations we observe in other beings like ourselves; and what we have to do is to examine the evidence which may bring home to our convictions the existence of this something that perceives, thinks, acts, originates new ideas; holds former ideas in consciousness, is connected with and acts upon and is acted on by bodily organs, and is at the same time more than and different from those organs.

I have referred to some of the mental phenomena which have the strongest tendency to prove the existence of the mind as an organized entity. These are the phenomena which occur in our waking hours, when the intellectual faculties and the bodily organs are in the full exercise of their normal functions respectively. There is another class of mental phenomena which may be said to be abnormal, in this, that the intellectual faculties and the bodily organs do not preserve the same relations to each other in all respects that they do when we are fully awake. These are the phenomena that occur during sleep—a class of mental phenomena of great consequence to be observed and analyzed in any study of psychology. They are of an extraordinary variety, complex in the highest degree, and dependent on numerous causes of mental and physical disturbance; but it is quite possible to extract from some of them certain definite conclusions.

Sleep, properly regarded, when it is perfect, is a state of absolute rest and inactivity of all the organs and functions of the body save the digestion of food and the circulation of the blood, and of all the mental faculties. Perfect sleep, sleep in which there is absolutely no consciousness, is more rare than those states in which there is more or less consciousness. But it is often an actual state of both body and mind, and it was evidently designed to renew the vigor of both, and to prevent the wear and tear of unbroken activity. Between absolute unconsciousness induced by perfect sleep and the full consciousness of our waking moments, there are many intermediate states; and the phenomena of these intermediate states present very strong proofs of the existence of the mind as a special and spiritual entity, capable in greater or less degree of acting without the aid of the physical organs. I do not except even the organ of the brain from this suspension of action during certain states when the mind is in more or less of activity; for I am convinced that in some of the mental phenomena to which I shall advert and which I shall endeavor to describe, the brain is in a state of perfect sleep, and that in the production of those phenomena it takes no part. In other mental phenomena, which occur during sleep, the brain or some part of it is evidently acted upon by the mind, as in the somnambulistic condition, when the nerves of motion, responding to the action of the mind, communicate action to the muscles, and the body walks about and performs other external acts.

There are other mental phenomena occurring during very profound sleep of the body and its organs, when the mind does not appear to derive its action from the brain, or to be dependent on the brain for its activity; when it is exceedingly active, and when it communicates action to none of the bodily organs; when, for example, it carries on long trains of thought, composes sentences, invents conversations, makes poetry and prose, and performs other intellectual processes. Distributed into classes, the most important mental phenomena occurring during sleep are the following:

First, and presenting perhaps the strongest proof of the mind's independence of all the bodily organs, is that whole class of mental phenomena in which, during profound sleep of the body, we carry on conversations, compose original matter in the form of oral or written discourse, which we seem to ourselves to be producing, and solve intellectual difficulties which have baffled us when awake, or imagine that we receive from an unexpected source important information that we are not conscious of having previously received.