'Archetype' defies simple definition. The word derives from a Greek compound of arche and tupos. Arche or 'first principle' points to the creative source, which cannot be represented or seen directly. Tupos, or 'impression', refers to any one of the numerous manifestations of the 'first principle' (Joseph Henderson, from ARAS Vol.1: Archetypal Symbolism p.viii). Jung himself spoke of the "indefiniteness of the archetype, with its multiple meanings" (Collected Works of CG Jung, 16:497), and had many different thoughts about archetypes throughout his professional life. Just as in the process of using this online site it is helpful to circle around the diverse meanings of a symbol, perhaps it would be helpful to circle around 'archetype' by looking at some of the ways Jung described it in his collected works (volume and paragraph are cited).
Ways of Naming the Archetype
The contents of the collective unconscious…are known as archetypes (CW9(1):4).
…we are dealing with archaic or--I would say—primordial types, that is, with universal images that have existed since the remotest times (CW9(1):5).
…archetypes probably represent typical situations in life (CW8:255).
…qualities that are not individually acquired but are inherited…inborn forms of "intuition," namely the archetypes of perception and apprehension, which are the necessary a priori determinants of all psychic processes (CW8:270).
It seems to me their origin can only be explained by assuming them to be deposits of the constantly repeated experiences of humanity (CW7:109).
How an Archetype Expresses Itself
The term 'archetype' is often misunderstood as meaning a certain definite mythological image or motif…on the contrary, [it is] an inherited tendency of the human mind to form representations of mythological motifs—representations that vary a great deal without losing their basic pattern…This inherited tendency is instinctive, like the specific impulse of nest-building, migration, etc. in birds. One finds the representations collectives practically everywhere, characterized by the same or similar motifs. They cannot be assigned to any particular time or region or race. They are without known origin, and they can reproduce themselves even where transmission through migration must be ruled out (CW 18:523).
…besides [the intellect] there is a thinking in primordial images—in symbols which are older than historic man, which are inborn in him from the earliest times, and, eternally living, outlasting all generations, still make up the groundwork of the human psyche (CW8:794).
As the products of imagination are always in essence visual, their forms must, from the outset, have the character of images and moreover of typical images, which is why…I call them 'archetypes' (CW 11:845).
…[Tribal] lore is concerned with archetypes that have been modified in a special way. Another well-known expression of the archetypes is myth and fairytale (CW 9 (1):5,6).
The archetype is essentially an unconscious content that is altered by becoming conscious and by being perceived, and it takes its color from the individual consciousness in which it happens to appear (CW 9(1):6).
The Archetype's Link with Ancestral Life
The collective unconscious comprises in itself the psychic life of our ancestors right back to the earliest beginnings. It is the matrix of all conscious psychic occurrences… (CW 8:230)
An archetype is like an old watercourse along which the water of life has flowed for centuries, digging a deep channel for itself (CW10:395).
…for the contents of the collective unconscious are not only residues of archaic, specifically human modes of functioning, but also the residues of functions from [our] animal ancestry, whose duration in time was infinitely greater than the relatively brief epoch of specifically human existence (CW 7:159).
The Value of the Archetype
It is only possible to live the fullest life when we are in harmony with these symbols; wisdom is a return to them (CW8:794).
[For the alchemists] they were seeds of light broadcast in the chaos…the seed plot of a world to come…One would have to conclude from these alchemical visions that the archetypes have about them a certain effulgence or quasi-consciousness, and that numinosity entails luminosity (CW8:388).
All the most powerful ideas in history go back to archetypes. This is particularly true of religious ideas, but the central concepts of science, philosophy, and ethics are no exception to this rule. In their present form they are variants of archetypal ideas created by consciously applying and adapting these ideas to reality. For it is the function of consciousness not only to recognize and assimilate the external world through the gateway of the senses, but to translate into visible reality the world within us (CW8, 342).