Consciousness. This is the most comprehensive term employed in designating the mind. In the widest and most unexceptionable meaning, consciousness is a term which includes all mental states, operations, or processes, and, as has been truly said, it is not strictly susceptible of definition, seeing that we can have no experience of the unconscious. We may specify different modes or varieties of consciousness, such as thoughts, feelings, and volitions; but the quality in which they all agree, and which constitutes them mental facts or states of consciousness, cannot be otherwise explained than by a mere reference to the constant experience of every human being. Consciousness, in this its strict sense, thus embraces the whole field of mental experience, and the expression 'facts of consciousness' is frequently used as synonymous with psychical facts or facts of mind to designate the subject-matter of psychology.
Popularly, therefore, when we are mentally alive, or performing any of the recognised functions of the mind, we are said to be conscious; while the total cessation of every mental energy is described by the term 'unconsciousness,' among other phrases. In dreamless sleep, in stupor, fainting, and under the influence of the anaesthetic drugs, we are unconscious; in waking, or rallying into renewed mental activity, we are said to become conscious.
The difficulties of the subject, however, have prevented a perfectly definite and uniform usage from being adhered to. As the mind in its waking or active condition may be more or less excited, or vary in the intensity of its manifestations, there are degrees of consciousness; and, accordingly, the name is apt to be applied to denote the higher degrees in opposition to the lower. Thus, in first learning to write, to cast up sums, to play on an instrument, or to ride a bicycle, our mind is put very much on the stretch; in other words, we are very much excited or highly conscious. But when years of incessant practice have consummated the process into a full-formed habit, a very small amount of mental attention is involved; and we may then be said to perform the work all but unconsciously. Such habitual actions are frequently designated secondarily automatic, and Sir W. Hamilton, for example, speaks in this connection of 'unconscious mental modifications.' But as he has previously defined consciousness as co-extensive with all mental phenomena, such a phrase evidently involves a contradiction in terms, being equivalent to unconscious consciousness. It is explained, though not justified, by the (unavowed) double use of the term consciousness just adverted to. Later writers have sought to escape from this inconvenient terminology by speaking of the more obscure mental processes as 'sub-conscious.' Stress is laid by them upon the infinite gradations of consciousness, and some amount of consciousness, however infinitesimal, is postulated so long as we can speak with propriety of mental phenomena at all. This sub-conscious region is understood to include not only the phenomena of habit referred to above, but the mass of organic or bodily feelings which, though intellectually unanalysed, are constantly present as a kind of background to our more distinct consciousness, and mainly determine both our habitual temperament and our varying moods. The hypothesis is also employed to explain the phenomena of memory as well as that instinctive basis of human life to which, under the name of the Unconscious, Hartmann (q.v.) has of late assigned such important philosophical functions.
Consciousness is sometimes used in a special sense to denote the mind's cognisance of itself, as opposed to the cognisance or examination of the outer world. Hence, in studying our own minds, we are said to be using consciousness as the instrument; but in studying minerals or plants, we resort to external observation by the senses. A contrast is thus instituted between consciousness and observation, which contrast gives to the former word a peculiarly contracted meaning; for in the wide sense above described, observation is truly an act of consciousness. But such a usage is confusing and undesirable, and has been generally abandoned by accurate writers. The study of our own mind may be more appropriately expressed by such phrases as 'self-consciousness,' 'reflection,' or 'introspection.'
Important philosophical points are involved in the determination of the conditions of consciousness, or the circumstances attendant on the manifestation of mental energy. The most general and fundamental condition of our becoming conscious is difference or change. The even continuance of one impression tends to unconsciousness; and there are a number of facts that show that if an influence were present in one unvarying degree from the first moment of life to the last, that influence would be to our feeling and knowledge as if it did not exist at all. This condition of our mental life has been formulated by Professor Bain as the Law of Relativity. For the varieties or divisions of our conscious states, see PSYCHOLOGY. See also PERSONALITY.