Humans succeed so well at using causes to achieve desired effects that David Hume’s assertion in 1739 still seems preposterous. He held that we cannot know the connection between cause and effect. We overlook the way we gain what knowledge we have. Success at particular efforts does not bring with it the knowledge of the necessary connection. Perhaps the shortest convincing proof is the observation that were we to know the connection we would be able to say how everything about us came about (Balzer, 1991).

Even in 1739 science had charted some causes remarkably well; Newton’s laws of momentum and his explanation of gravity had become old knowledge by then. Technology had made the industrial revolution a superb demonstration of man mastering cause and effect. How could a citizen of the 21st century accept Hume’s assertion? And yet over the dinner table the conversation had turned on our ignorance of what caused an effect that troubled her greatly. Her son had become depressed. Looking at the effect, could the Psychology Industry divine the cause and provide the cure? It certainly claims to do so and his psychiatrist was trying. The track record of psychiatry illustrates its failure. The amount of antidepressants dispensed over the past two decades had increased enormously at the same time that the diagnosis of  depressive illness grew eightfold.

It took centuries for Hume’s reputation to grow. In his own time he had not escaped attention. He upset many. They branded his ideas as heresy at a time when burning at the stake remained the cure. Not until the 20th century did his ideas begin to exert their deserved influence. His take on economic policy influenced great makers and shakers such as the Iron Lady. His ideas have still more unrealised potential. I propose that his formulation of the connection between cause and effect be recognised as Hume’s law. It defines a limit that reason only too readily ignores.

Hume explained that we can only find that in each single instance an effect follows a cause, the sequence known as antecedent to consequent. Scientists hold to that sequence in experiment. Likewise our knowledge depends on the experience that the sequence imposes. Experience and experiment  demand the “PRIORITY of time in the cause before the effect.”

Psychiatry and the law, indeed much common reason, readily ignores the principle. All who reason backwards from effects to discern the cause do so. Psychiatrists identify mental illness from effects (consequents), the complaints or symptoms that patients proffer. The law does the same when a court takes as sufficient proof of cause be the work done before the complaints appear. It reasons backwards from consequent to antecedent. In this way psychiatry and the law evade the discipline of experimental proof that observes Hume’s law. In doing so they succumb to current belief and prejudice. Antecedent prejudice impelled the outrageous conviction of Lindy Chamberlain and other innocents (see “The Disadvantage of Innocence” in Chap.5 of “Welcome to the Loony Bin“). It shapes a great many awards of compensation for pseudo-illness (also in Chap.5 see “Epidemic Pseudo-Illness”), thereby penalising employers and other innocents and undermining the economic health of the nation.