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Valentine’s concept of introversion includes traits that contemporary psychology would classify as openness to experience (“thinker, dreamer”), conscientiousness (“idealist”), and neuroticism (“shy individual”).
A long line of poets, scientists, and philosophers have also tended to group these traits together. All the way back in Genesis, the earliest book of the Bible, we had cerebral Jacob (a “quiet man dwelling in tents” who later becomes “Israel,” meaning one who wrestles inwardly with God) squaring off in sibling rivalry with his brother, the swashbuckling Esau (a “skillful hunter” and “man of the field”). In classical antiquity, the physicians Hippocrates and Galen famously proposed that our temperaments—and destinies—were a function of our bodily fluids, with extra blood and “yellow bile” making us sanguine or choleric (stable or neurotic extroversion), and an excess of phlegm and “black bile” making us calm or melancholic (stable or neurotic introversion). Aristotle noted that the melancholic temperament was associated with eminence in philosophy, poetry, and the arts (today we might classify this as opennessto experience). The seventeenth-century English poet John Milton wrote Il Penseroso (“The Thinker”) and L’Allegro (“The Merry One”), comparing “the happy person” who frolics in the countryside and revels in the city with “the thoughtful person” who walks meditatively through the nighttime woods and studies in a “lonely Towr.” (Again, today the description of Il Penseroso would apply not only to introversion but also to openness to experience and neuroticism.) The nineteenth-century German philosopher Schopenhauer contrasted “good-spirited” people (energetic, active, and easily bored) with his preferred type, “intelligent people” (sensitive, imaginative, and melancholic). “Mark this well, ye proud men of action!” declared his countryman Heinrich Heine. “Ye are, after all, nothing but unconscious instruments of the men of thought.”
Because of this definitional complexity, I originally planned to invent my own terms for these constellations of traits. I decided against this, again for cultural reasons: the words introvert and extrovert have the advantage of being well known and highly evocative. Every time I uttered them at a dinner party or to a seatmate on an airplane, they elicited a torrent of confessions and reflections. For similar reasons, I’ve used the layperson’s spelling of extrovert rather than the extravert one finds throughout the research literature.
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