Again and again I encounter the mistaken notion that an archetype is determined in regard to its content, in other words that it is a kind of unconscious idea (if such an expression be admissible). It is necessary to point out once more that archetypes are not determined as regards their content, but only as regards their form and then only to a very limited degree. A primordial image is determined as to its content only when it has become conscious and is therefore filled out with the material of conscious experience. Its form, however, as I have explained elsewhere, might perhaps be compared to the axial system of a crystal, which, as it were, preforms the crystalline structure in the mother liquid, although it has no material existence of its own. This first appears according to the specific way in which the ions and molecules aggregate. The archetype in itself is empty and purely formal, nothing but a facultas praeformandi, a. possibility of representation which is given a priori. The representations themselves are not inherited, only the forms, and in that respect they correspond in every way to the instincts, which are also determined in form only. The existence of the instincts can no more be proved than the existence of the archetypes, so long as they do not manifest themselves concretely. With regard to the definiteness of the form, our comparison with the crystal is illuminating inasmuch as the axial system determines only the stereometric structure but not the concrete form of the individual crystal. This may be either large or small, and it may vary endlessly by reason of the different size of its planes or by the growing together of two crystals. The only thing that remains constant is the axial system, or rather, the invariable geometric proportions underlying it. The same is true of the archetype. In principle, it can be named and has an invariable nucleus of meaning-but always only in principle, never as regards its concrete manifestation. In the same way, the specific appearance of the mother-image at any given time cannot be deduced from the mother archetype alone, but depends on innumerable other factors.
— Carl Gustav Jung
Jung reaches for the crystal not as decoration but as precision. What he is correcting matters: the archetype is not an idea waiting in the dark, not a template that stamps its image onto experience, not a Platonic form that the soul merely recovers. It is prior to content — an axial system that has no material existence of its own, that preforms a structure in the mother liquid before any molecule has settled into place. The form is real, the representation is not yet.
This distinction carries more weight than it first appears to. If the archetype were content-determined, you could in principle retrieve it — purify the mother-image back to the Mother, strip the specific father down to the Father. The crystal analogy closes that door. No two crystals grow identically even when the axial logic is identical; the planes vary, the size varies, two crystals sometimes grow together and produce something neither axial system alone could have predicted. What you actually encounter in a patient, in a dream, in your own nightly imagery, is always a singular crystallization — never the archetype in itself, only one of its possible concrete manifestations, shaped by everything else in the mother liquid at that moment.
The practical consequence is that interpretation is never deduction. You cannot read the mother archetype and thereby know the mother-image. You have to look at what grew.
Carl Gustav Jung·The Archetypes and the Collective Unconscious·1959