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THE TERM “conspiracy theory” commonly means a fringe theory that explains an event as the secret machinations of powerful Machiavellian conspirators. The modern popularity of such theories dates from the conspiracy theory that arose in the 1960s around the assassination of JFK. Mainstream opinion looks on conspiracy theories with a jaundiced eye and often ridicules them. Of course genuine conspiracies do exist, for example Abraham Lincoln died as a result of a conspiracy. And George Bernard Shaw said, “All professions are conspiracies against the laity”.

The word “theory” in “conspiracy theory” is used in a different sense to its use in science. A scientific theory is the agreed best explanation of a phenomenon, arrived at after long years of examining evidence and testing hypotheses by experiment. In everyday usage theory refers to a hypothesis – an informed (and sometimes not-informed) guess as to the explanation of a phenomenon. Scientific theories are falsifiable and modifiable in the light of new evidence. Conspiracy theories, eg a secret branch of government is covering-up evidence of alien visits, are often unfalsifiable. Proponents of conspiracy theories are also very resistant to contrary evidence.