In our yoga we mean by the subconscient that quite submerged part of our being in which there is no wakingly conscious and coherent thought, will or feeling or organized reaction, but which yet receives obscurely the impressions of all things and stores them up in itself and from it too all sorts of stimuli, of persistent habitual movements, crudely repeated or disguised in strange forms can surge up into dream or into the waking nature. For if these impressions rise up most in dream in an incoherent and disorganized manner, they can also and do rise up into our waking consciousness as a mechanical repetition of old thoughts, old mental, vital and physical habits or an obscure stimulus to sensations, actions, emotions which do not originate in or from our conscious thought or will and are even often opposed to its perceptions, choice or dictates. In the subconscient there is an obscure mind full of obstinate Sanskaras, impressions, associations, fixed notions, habitual reactions formed by our past, an obscure vital full of the seeds of habitual desires, sensations and nervous reactions, a most obscure material which governs much that has to do with the condition of the body. It is largely responsible for our illnesses; chronic or repeated illnesses are indeed mainly due to the subconscient and its obstinate memory and habit of repetition of whatever has impressed itself upon the body-consciousness. But this subconscient must be clearly distinguished from the subliminal parts of our being such as the inner or subtle physical consciousness, the inner vital or inner mental; for these are not at all obscure or incoherent or ill-organized, but only veiled from our surface consciousness. Our surface constantly receives something, inner touches, communications or influences, from these sources but does not know for the most part whence they come.
—Sri Aurobindo, Letters on Yoga, p. 360
That part of us which we can strictly call subconscient because it is below the level of mind and conscious life, inferior and obscure, covers the purely physical and vital elements of our constitution of bodily being, unmentalised, unobserved by the mind, uncontrolled by it in their action. It can be held to include the dumb occult consciousness, dynamic but not sensed by us, which operates in the cells and nerves and all the corporeal stuff and adjusts their life process and automatic responses. It covers also those lowest functionings of submerged sense-mind which are more operative in the animal and in plant life; in our evolution we have overpassed the need of any large organised action of this element, but it remains submerged and obscurely at work below our conscious nature. This obscure activity extends to a hidden and hooded mental substratum into which past impressions and all that is rejected from the surface mind sink and remain there dormant and can surge up in sleep or in any absence of the mind, taking dream forms, forms of mechanical mind action or suggestion, forms of automatic vital reaction or impulse, forms of physical abnormality or nervous perturbance, forms of morbidity, disease, unbalance. Out of the subconscious we bring ordinarily so much to the surface as our waking sense-mind and intelligence need for their purpose; in so bringing them up we are not aware of their nature, origin, operation and do not apprehend them in their own values but by a translation into the values of our waking human sense and intelligence. But the risings of the subconscious, its effects upon the mind and body, are mostly automatic, uncalled for and involuntary; for we have no knowledge and therefore no control of the subconscient. It is only by an experience abnormal to us, most commonly in illness or some disturbance of balance, that we can become aware of something in the dumb world, dumb but very active, of our bodily being and vitality or grow conscious of the secret movements of the mechanical subhuman physical and vital mind which underlies our surface, — a consciousness which is ours but seems not ours because it is not part of our known mentality. This and much more lives concealed in the subconscience.
A descent into the subconscient would not help us to explore this region, for it would plunge us into incoherence or into sleep or a dull trance or a comatose torpor. A mental scrutiny or insight can give us some indirect and constructive idea of these hidden activities; but it is only by drawing back into the subliminal or by ascending into the superconscient and from there looking down or extending ourselves into these obscure depths that we can become directly and totally aware and in control of the secrets of our subconscient physical, vital and mental nature. This awareness, this control are of the utmost importance. For the subconscient is the Inconscient in the process of becoming conscious; it is a support and even a root of our inferior parts of being and their movements. It sustains and reinforces all in us that clings most and refuses to change, our mechanical recurrences of unintelligent thought, our persistent obstinacies of feeling, sensation, impulse, propensity, our uncontrolled fixities of character. The animal in us, — the infernal also, — has its lair of retreat in the dense jungle of the subconscience. To penetrate there, to bring in light and establish a control, is indispensable for the completeness of any higher life, for any integral transformation of the nature.
—Sri Aurobindo, The Life Divine, p. 762