Eysenck and the Four Temperaments
How a 20th-century psychologist turned the ancient theory of four humors into a measurable map of personality — and what sanguine, choleric, melancholic and phlegmatic actually mean.
Around 2,000 years before personality psychology existed, Greek physicians believed your character was determined by the balance of four bodily fluids — blood, yellow bile, black bile, and phlegm. The theory was medically worthless. And yet the four personality portraits it produced — the cheerful sanguine, the fiery choleric, the brooding melancholic, and the calm phlegmatic — refused to die, because people kept recognising themselves in them.
Hans Eysenck (1916–1997), a German-born British psychologist and one of the most cited researchers in the history of the field, explained why. The ancient portraits survived because they accidentally described something real — not fluids, but the two most fundamental dimensions along which human temperaments differ.
The Two Axes
Extraversion–Introversion describes where your energy flows and how much stimulation your brain wants. Eysenck argued extraverts have a chronically under-aroused cortex — they seek people, noise, and risk to reach a comfortable level of stimulation. Introverts run over-aroused — the same party that energises an extravert overloads them.
Neuroticism–Stability describes how strongly your nervous system responds to threat. High-neuroticism brains sound the alarm earlier, louder, and longer — producing worry, mood swings, and rumination. Stable temperaments have a slower, quieter alarm that resets fast.
Cross the two axes and you get four quadrants — and they map precisely onto the ancient portraits: stable extravert = sanguine, unstable extravert = choleric, unstable introvert = melancholic, stable introvert = phlegmatic. The Greeks had the right map and the wrong mechanism.
From the EPI to Modern Science
Eysenck built questionnaires to measure his dimensions — the Eysenck Personality Inventory (EPI) and later the EPQ, which added a third dimension, psychoticism (tough-mindedness). His instruments became some of the most widely used in psychology. The field eventually settled on the five-factor "Big Five" model, but tellingly, both of Eysenck's original axes survived inside it almost unchanged as Extraversion and Neuroticism. Whatever else personality science argues about, these two dimensions are its bedrock.
The Four Temperaments Today
No one is a pure type — the quadrants are regions on a continuous map, and most people live near a border. But knowing your home quadrant answers two practical questions better than most self-help does: how do you recharge (people or solitude), and how does your alarm system behave under pressure (loud or quiet). Those two facts explain a remarkable amount of friction in work, relationships, and rest.