From the Introduction to
Psychological Types:
[Extraverts and introverts] are so different and present such a striking contrast that their existence becomes quite obvious even to the layman once it has been pointed out. 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 on good terms with everybody, or quarrel with everybody, but always relate to them in some way and in turn are affected by them.
From
Psychological Typology, a 1936 article:
[The introvert] holds aloof from external happenings, does not join in, has a distinct dislike of society as soon as he finds himself among too many people. In a large gathering he feels lonely and lost. ... He is not in the least "with it," and has no love of enthusiastic get-togethers. He is not a good mixer. What he does, he does in his own way, barricading himself against influences from outside. He is apt to appear awkward, often seeming inhibited, and it frequently happens that, by a certain brusqueness of manner, or by his glum unapproachability, or some kind of malapropism, he causes unwitting offence to people. His better qualities he keeps to himself, and generally does everything he can to dissemble them. He is easily mistrustful, self-willed, often suffers from inferiority feelings and for this reason is also envious. His apprehensiveness of the object is not due to fear, but to the fact that it seems to him negative, demanding, overpowering or even menacing. He therefore suspects all kinds of bad motives, has an everlasting fear of making a fool of himself, is usually very touchy and surrounds himself with a barbed wire entanglement so dense and impenetrable that finally he himself would rather do anything than sit behind it. ...
For him self-communings are a pleasure. His own world is a safe harbour, a carefully tended and walled-in garden, closed to the public and hidden from prying eyes. His own company is the best. He feels at home in his world, where the only changes are made by himself. His best work is done with his own resources, on his own initiative, and in his own way. ...
His relations with other people become warm only when safety is guaranteed, and when he can lay aside his defensive distrust. All too often he cannot, and consequently the number of friends and acquaintances is very restricted.
From Chapter 6 of
Psychological Types:
The [introvert's] personality seems inhibited, absorbed or distracted, "sunk in thought," intellectually lopsided, or hypochondriacal. In every case there is only a meagre participation in external life and a distinct tendency to solitude and fear of other people, often compensated by a special love of animals or plants. ...
The [introvert's] sudden explosions [of emotion], alternating with defensiveness and periods of taciturnity, can give the personality such a bizarre appearance that such people become an enigma to everyone in their vicinity. Their absorption in themselves leaves them at a loss when presence of mind or swift action is demanded. Embarrassing situations often arise from which there seems no way out—one reason the more for shunning society. Moreover the occasional outbursts of affect play havoc with their relations to others, and, because of their embarrassment and helplessness, they feel incapable of retrieving the situation. This awkwardness in adapting leads to all sorts of unfortunate experiences which inevitably produce a feeling of inferiority or bitterness, and even of hatred that is readily directed at those who were the actual or supposed authors of their misfortunes. ... They have a peculiar emotional sensitivity, revealing itself to the outside world as a marked timidity and uneasiness in the face of emotional stimuli, and in all situations that might evoke them. This touchiness is directed primarily against the emotional conditions in their environment. All brusque expressions of opinion, emotional declarations, playing on the feelings, etc., are avoided from the start, prompted by the subject's fear of his own emotion, which in turn might start off a reverberating impression he might not be able to master. This sensitivity may easily develop over the years into melancholy, due to the feeling of being cut off from life.
From the above-mentioned 1936 article:
Extraversion is characterized by interest in the external object, responsiveness, and a ready acceptance of external happenings, a desire to influence and be influenced by events, a need to join in and get "with it," the capacity to endure bustle and noise of every kind, and actually find them enjoyable, constant attention to the surrounding world, the cultivation of friends and acquaintances, none too carefully selected, and finally by the great importance attached to the figure one cuts, and hence by a strong tendency to make a show of oneself. Accordingly, the extravert's philosophy of life and his ethics are as a rule of a highly collective nature with a strong streak of altruism, and his conscience is in large measure dependent on public opinion. Moral misgivings arise mainly when "other people know." His religious convictions are determined, so to speak, by majority vote. ...
The disinclination to submit his own motives to critical examination is very pronounced. He has no secrets he has not long since shared with others. Should something unmentionable nevertheless befall him, he prefers to forget it. Anything that might tarnish the parade of optimism and positivism is avoided. Whatever he thinks, intends, and does is displayed with conviction and warmth. ...
The psychic life of this type of person is enacted, as it were, outside himself, in the environment. He lives in and through others; all self-communings give him the creeps. Dangers lurk there which are better drowned out by noise. If he should ever have a "complex," he finds refuge in the social whirl and allows himself to be assured several times a day that everything is in order. Provided he is not too much of a busybody, too pushing, and too superficial, he can be a distinctly useful member of the community.
but actually I still am not 100% sure how to reason about P dominant behavior, although people have been very helpful 
True dichotomies are a more elegant theory. A spectrum, especially if it's normally distributed sais very little about the population.
