In contrast to the personal unconscious, which is a relatively thin layer immediately below the threshold of consciousness, the collective unconscious shows no tendency to become conscious under normal conditions, nor can it be brought back to recollection by any analytical technique, since it was never repressed or forgotten.
The collective unconscious is not to be thought of as a self-subsistent entity; it is no more than a potentiality handed down to us from primordial times in the specific form of mnemonic images3 or inherited in the anatomical structure of the brain.
There are no inborn ideas, but there are inborn possibilities of ideas that set bounds to even the boldest fantasy and keep our fantasy activity within certain categories: a priori ideas, as it were, the existence of which cannot be ascertained except from their effects.
They appear only in the shaped material of art as the regulative principles that shape it; that is to say, only by inferences drawn from the finished work can we reconstruct the age-old original 4 of the primordial image. ~Carl Jung, CW 15, Para 126