C. G. Jung, the famous psychologist, coined the terms “introvert” and “extravert,” but writers had been creating introverted and extraverted characters for centuries. Shakespeare’s Prince Hamlet, for example, is an obvious introvert whose primary conscious “function,” using another Jungian term, is thinking. Samuel Taylor Coleridge expressed the opinion that Hamlet’s “problem,” the character trait which prevented him from carrying out his intention and duty to kill King Claudius was that he thought too much.
In his book Psychological Types, Jung discusses the type whose “attitude” is introversion and whose sovereign conscious “function” is thinking. What is significant in trying to account for Hamlet’s “indecisiveness” can be found in the following passages from Jung’s difficult but fascinating and highly influential book.
Closer investigation shows with great regularity that, besides the most differentiated function [in our case, Hamlet’s thinking], another, less differentiated function of secondary importance is invariably present in consciousness and exerts a co-determining influence. [The other three conscious functions are intuition, sensation, and feeling.]….Naturally only those functions can appear as auxiliary whose nature is not opposed to the dominant function. For instance, feeling can never act as the second function alongside thinking, because it is by its very nature too strongly opposed to thinking. Thinking, if it is to be real thinking and true to its own principle, must rigorously exclude feeling.
This seems to provide the best explanation of the so-called Hamlet problem. Why doesn’t Hamlet simply kill Claudius the first chance he gets? Hamlet asks himself that question, notably in his soliloquy in Act 2, Scene 2, in which he berates himself for his failure to act. For example:
Why, what an ass am I! This is most brave,
That I, the son of a dear father murdered,
Prompted to my revenge by heaven and hell,
Must like a whore unpack my heart with words,
And fall a-cursing like a very drab,
Hamlet’s problem, to refer back to Jung, is that his thinking “must rigorously exclude feeling”—and without feeling murderous rage he cannot commit a murder. Whenever he does act decisively--as when he kills Polonius, when he boards the pirate ship, and when he grapples with Laertes in Ophelia’s grave—it is always before he has had a chance to think. When he finally kills Claudius it is when his normally repressed feelings have taken precedence over this introverted thoughtful nature.
…feeling can never act as the second function alongside thinking, because it is by its very nature too strongly opposed to thinking. Thinking, if it is to be real thinking and true to its own principle, must rigorously exclude feeling.
The reverse would be true of a person whose dominant conscious function was feeling. Feeling would rigorously exclude thinking. We have all known people of both types—those who appear unfeeling and those who appear unthinking.
The article on Psychological Types in Wikipedia explains Jung’s classifications in detail. See also the Wikipedia article on the modern Myers-Briggs Type Indicator, which was extrapolated from Jung’s Psychological Types, by consulting the reference links below.