We can construct a typology of rumours - defined broadly as unverified news - according to their relation to reality after their degree of veracity has been established, at least in the current state of knowledge, by experts (historians, scientists, police officers, journalists, and so on). If a rumour turns out to be correct it becomes an item of information. If a rumour is untrue it comes into the categories of affirming or denying rumours. Affirming rumours, which are the most common type, state the reality of imaginary facts, for instance the rumour claiming that bananas from Costa Rica pass on to people flesh-eating bacteria that cause general necrosis. Denying rumours, which are rarer, deny the reality of established facts, for example rumours claiming that Elvis Presley is not dead or that Americans have never walked on the moon.

It seems useful to distinguish various terms indicating negation. Rumours will be termed negative when they state facts associated with fear or hostility, whereas positive rumours evoke happy, welcome events. French researchers, who assign colours to rumours, talk about ‘black’ rumours or ‘rose-tinted’ ones. Specialists agree that there are around nine black rumours for every rose-tinted one. Rouquette (1975, 1990) has thoroughly studied this ‘bias towards negativity’, which is one of the main features of rumours. I shall talk about denying rumours and ideas when they deny commonly accepted events. These rumours are not necessarily negative: for instance survival legends often express the wish that a loved person were not dead. Finally, among denying rumours and ideas, we shall reserve the word negationist for revisionist claims that the gas chambers did not exist, or that a Nazi did not plan to exterminate the Jews during the Second World War.