No organism can afford to be conscious of matters with which it could deal at unconscious levels. Broadly, we can afford to sink those sorts of knowledge which continue to be true regardless of changes in the environment, but we must maintain in an accessible place all those controls of behavior which must be modified for every instance. The economics of the system, in fact, pushes organisms toward sinking into the unconscious those generalities of relationship which remain permanently true and toward keeping within the conscious the pragmatic of particular instances.
Up till now [the development of proto-consciousness], we can suppose, nervous systems solved the "Now what do I do?" problem by a relatively simple balancing act between a strictly limited repertoire of actions — if not the famous four F's (fight, flee, feed, or mate), then a modest elaboration of them.
I think of consciousness as a bottomless lake, whose waters seem transparent, yet into which we can clearly see but a little way.But in this water there are countless objects at different depths; and certain influences will give certain kinds of those objects an upward influence which may be intense enough and continue long enough to bring them into the upper visible layer. After the impulse ceases they commence to sink downwards.
Consciousness surely does not depend on language. Babies, many animals, and patients robbed of speech by brain damage are not insensate robots; they have reactions like ours that indicate that someone's home.
Our whole past experience is continually in our consciousness, though most of it sunk to a great depth of dimness. I think of consciousness as a bottomless lake, whose waters seem transparent, yet into which we can clearly see but a little way.