Introduction

Carl Gustav Jung (July 26, 1875 – June 6, 1961) wrote in Psychological Types¹:

Everyone knows those reserved, inscrutable, rather shy people who form the strongest possible contrast to the open, sociable, jovial, or at least friendly and approachable characters who are in good terms with everybody, or quarrel with everybody, but always relate to them in some way and in turn are affected by them. (…)

The introvert's attitude is an abstracting one; at bottom, he is always intent on withdrawing libido from the object, as through he had to prevent the object from gaining power over him. The extrovert, on the contrary, has a positive relation to the object. He affirms its importance to such an extent that his subjective attitude is constantly related to and oriented by the object. The object can never have enough value for him, and its importance must always be increased. (…)

The relation between subject and object, biologically considered, is always one of adaptation (…) There are in nature two fundamentally different modes of adaptation which ensure the continued existence of the living organism. The one consists in a high rate of fertility, with low powers of defence and short duration of life for the single individual; the other consists in equipping the individual with numerous means of self-preservation plus a low fertility rate. (… The) peculiar nature of the extrovert constantly urges him to expend and propagate himself in every way, while the tendency of the introvert is to defend himself against all demands from outside, to conserve his energy by withdrawing it from objects, thereby consolidating this own position. (…) Just as, biologically, the two modes of adaptation work equally well and are successful in their own way, so too with the typical attitudes. The one achieves its end by a multiplicity of relationships, the other by monopoly