Phlegm and nonsense

Some ideas are just wrong. Others are utterly wrong, outrageously wrong, stupidly wrong, maliciously wrong or, as Wolfgang Pauli once said in demolishing a very weak theory, "not even wrong". The theory of the humours is interestingly wrong, and perhaps also, to use 1066 and All That 's description of the Cavaliers, "wromantic but wrong".

The elegant, beautiful, intellectually satisfying theory of the humours held sway over medicine, philosophy and the arts for two millennia, having every virtue except that of being empirically correct. Empedocles, codifying earlier Greek thinking on the precise number of elements, suggested that everything was made from earth, water, fire and air. This conceptualisation, with earth opposing air and fire opposing water, incorporated Alcmaeon's psychologically astute observation that "most human affairs go in pairs". Each element also had two attributes, as did the corresponding humour: air and blood were hot and moist, water and phlegm were cold and moist, fire and bile were hot and dry, and earth and the mysterious black bile - the melaina chole - were cold and dry.

Almost any aspect of life fitted into this scholastic Sudoku, with each row, column and quadrant having its humour, be it childhood, youth, adulthood and old age, the four seasons, or the humoural imbalance that - as Chaucer's physician knew from "Ypocras... and Galien" - was "the cause of everich maladye, were it of hoot or cold, or moiste or drye".

Later incorporations included the planets, the musical modes, and even taste preferences - the phlegmatic liking sweet, the sanguine salt, the choleric bitter and the melancholic sour. In the 18th century Lavater illustrated the physiognomies associated with each personality type. Much here is reminiscent of Popper's non-falsifiable bêtes noires of Marxism, astrology, homoeopathy and Ptolemy's planetary theory - with any minor deviation being resolved with an additional epicycle or two.

Noga Arikha's well-written history of the humours extends from its Classical origins, its development in Byzantine and Arab thought, its Renaissance flowering through to its collapse under the cold gaze of scientific method.

Arikha emphasises how intellectually impressive was Galen, "lucidly explain[ing] the visible through a series of brilliant, logical conjectures". Crude criticisms that the humours were not directly observed missed the point, with Arikha noting that "secretions are, precisely, secret". For William Harvey it was Galen's lack of actual dissection that made the theory "a universal syllogism on the basis of a particular proposition", and for Thomas Tryon, merely "Forms and Words, rather than Realities". How was such a theory of any practical use? Here Arikha is compelling, emphasising that, however imperfect, "one needs a map to make sense of bloody, decomposing organs".

The persistence of the theory of the humours reminds us that it met intellectual and cognitive needs, and for Arikha there is a "constancy in the structure of inductive explanation", so that the "explanatory structure has remained". Indeed, it is not difficult to find formal similarities between the fourfold elements and humours and Dalton's atomic theory, Mendeleev's periodic table, or modern theories invoking quarks, leptons, strings and supersymmetries.

Arikha's later chapters try to argue that although "the old humours are gone... they still serve as useful, suggestive and malleable images", that clandestinely continue in modern medicine.

However, it is unconvincing to say that "the original four humours... have been multiplied by the hundreds into hormones, enzymes, neurotransmitters, particles and the like, constituting the hydraulic system that is our body".

Maybe, but by now there is no longer any useful similarity, and superficial accounts of psychoneuroimmunology, neuropsychology, placebo effects and Eysenckian two-factor theories of personality do little to reassure. If the theory of the humours does survive, the author may be right to identify it not in the detailed mechanisms of modern medicine, but rather in alternative medicine's forces, fields and energies, and their excesses, deficits and balances, ideas that appeal to so many people.

Such flatulent pseudo-theorising, as Arikha says, supports "an entire industry that sustains the Hippocratic conceits of diet, exercise and air for the pursuit of health", with its echoes of the holism of Hippocrates' On Airs, Waters and Places .

In medicine, the humours have been entirely replaced by "revolting but right" molecular genetics, with its sequences of pyrimidines and purines and its puerile protein names.

While Ben Jonson's audience for Every Man Out of His Humour recognised "choler, melancholy, phlegm and blood", it has not escaped our notice that modern audiences and playwrights are unlikely to find either aesthetic inspiration or comedy in molecular genetics.

Chris McManus is professor of psychology and medical education at University College London.