In his unfinished Summa Theologica, Thomas Aquinas writes that madness is affected by the phases of the moon.
The Moon and Lunacy
There are similar stories about increases in the number of births, the number of suicides, the number of accidents and the number of violent crimes. There's even a variant which says there is a strong correlation between full Moons and prison riots.
The thread that binds all these myths together is that the Moon, more particularly the full Moon, powerfully influences human behaviour and human physiology.
Like most enduring myths, those about madness and the Moon have a small grain of truth. It is certainly true that scientists - especially in the US - have done some serious research on this subject. There are dozens of properly conducted and controlled scientific tests to determine whether or not the Moon has any effect on human - or animal - behaviour and biology.
But the vast majority of these researches have concluded that there is no correlation whatsoever between the Moon and changes in human behaviour. One small study did find that fewer women were likely to be admitted to hospital emergency rooms with overdoses during a full Moon, but the difference in numbers was very small.
What the studies did find was that there is a persistent and widespread belief among psychiatric nurses, hospital staff, policemen and prison warders that there is some sort of link between the full Moon and abnormal behaviour.
Why this should be so is still a matter for speculation. The best answer to date suggests that some people expect to see higher levels of abnormal human behaviour when there's a full Moon, and their expectations trick them into believing that there is a link even though the statistics do not bear it out.
The origins of 'lunacy'
The words 'lunacy' and 'lunatic' stem from the Latin word luna, meaning 'Moon', and the Roman goddess Luna, and the modern preoccupation with the effects of the Moon has its origins in the beliefs of the past.
The ancient Greeks had a scientific approach to madness. They believed that madness was caused by too much moisture in the brain. The great ancient Greek physician, Hippocrates (c 460 - c 370 BC), stated emphatically that 'madness comes from the brain's moistness'. Aware of the Moon's effects on tides, both the Greeks and Romans believed that the Moon also affected moisture and therefore had some effect on madness.
However, the very specific links between the Moon and madness seem to have been forged in the dark ages, and by the 13th century the great Italian theologian and philosopher St Thomas Aquinas (1226-1274) had combined the Greek scientific view of madness with medieval superstition. Aquinas wrote that madness was simultaneously caused by both demons and the effect of the Moon:
'That demons harass men according to certain phases of the Moon happens in two ways ... it is manifest that ''the brain is the most moist of all parts of the body," as Aristotle says. Therefore it is the most subject to the action of the Moon, the property of which is to move what is moist.' (Summa Theologica)
The earliest use of the word 'lunatic' in English literature occurs in William Langland's 14th-century poem, Vision Concerning Piers Plowman:
'Lunatic lollers and lepers about,
And mad as the Moon, some more or less'
By the time of the Renaissance in the sixteenth and seventeenth centuries, lunacy was no longer seen as some kind of demonic infestation but instead as a disease both caused and influenced by the phases of the Moon. In 1643, the natural philosopher John Swan wrote:
'This disease of lunacie, is a disease whose distemper followeth the course of the Moon.' (Speculum Mundi, or a Glass Representing the Face of the World)
This view continued to be held - albeit in a watered-down form - right up to the 19th century and beyond. From the middle of the 18th century onwards, people stopped believing that the Moon was the cause of madness. But they were still convinced that the Moon exacerbated madness. In his Pocket Encyclopaedia of 1827, T F Forster wrote:
'When the Moon is on the full, or new, people are more irritable than at other times ... Insanity at these times has its worst paroxysms.'
The 'biological tide theory'
The 20th-century revolution in attitudes to mental illness has meant that few psychiatrists now believe that mental illness is caused or affected by the Moon. But some scientists and popular psychologists are still convinced that the Moon affects human behaviour or biology.
The most popular theory - which has yet to be proved - is the 'biological tide theory'. Simply put, this argues that both the Earth's surface and human bodies are composed of the same materials in the same proportions - about 80% water and about 20% organic and inorganic matter. So just as the gravitational force of the Moon produces tides in the seas, so it produces biological tides in the human body which can affect the brain.
In fact, the biological tide theory is not dissimilar to the ancient Greek view that madness is caused by an excess of moisture in the brain. It seems that things have come full circle.
