We shall probably get nearest to the truth if we think of the conscious and personal psyche as resting upon the broad basis of an inherited and universal psychic disposition which is as such unconscious, and that our personal psyche bears the same relation to the collective psyche as the individual to society.
But equally, just as the individual is not merely a unique and separate being, but is also a social being, so the human psyche is not a self-contained and wholly individual phenomenon, but also a collective one.
And just as certain social functions or instincts are opposed to the interests of single individuals, so the human psyche exhibits certain functions or tendencies which, on account of their collective nature, are opposed to individual needs.
The reason for this is that every man is born with a highly differentiated brain and is thus assured of a wide range of mental functioning which is neither developed ontogenetically nor acquired.
But, to the degree that human brains are uniformly differentiated, the mental functioning thereby made possible is also collective and universal.
This explains, for example, the interesting fact that the unconscious processes of the most widely separated peoples and races show a quite remarkable correspondence, which displays itself, among other things, in the extraordinary but well-authenticated analogies between the forms and motifs of autochthonous myths.
The universal similarity of human brains leads to the universal possibility of a uniform mental functioning.
This functioning is the collective psyche.
Inasmuch as there are differentiations corresponding to race, tribe, and even family, there is also a collective psyche limited to race, tribe, and family over and above the “universal” collective psyche.
To borrow an expression from Pierre Janet, the collective psyche comprises the parties infirieures of the psychic functions, that is to say those deep-rooted, well-nigh automatic portions of the individual psyche which are inherited and are to be found everywhere, and are thus impersonal or supra-personal.
Consciousness plus the personal unconscious constitutes the parties superieures of the psychic functions, those portions, therefore, that are developed ontogenetically and
Consequently, the individual who annexes the unconscious heritage of the collective psyche to what has accrued to him in the course of his ontogenetic development, as though it were part of the latter, enlarges the scope of his personality in an illegitimate way and suffers the consequences.
In so far as the collective psyche comprises the parties inferieures of the psychic functions and thus forms the basis of every personality, it has the effect rushing and devaluing the personality.
This shows itself either in the aforementioned stifling of self-confidence or else in an unconscious heightening of the ego’s importance to the point of a pathological will to power. ~Carl Jung; The Portable Jung; Pages 93-94.