The September 11, 2001, attacks set off a wave of conspiracy theories. Credit:Reuters It is widely argued that the coming of the internet has been the main force behind the spread of such theories, and that they are undermining trust in political systems – even causing people increasingly to question the fundamentals of our democracy. In the US, for example, trust in President Barack Obama has been undermined by the spread of the idea that he and Democrats have conspired to cover up the fact that he was not born in America and was therefore not eligible for election. The Bilderberg Group of senior world statesmen is, it is believed, a cover-up for the creation of a New World Order, in which national democracies are being replaced by a global dictatorship. British Prime Minister David Cameron is allegedly part of the plot, connected through his wife's stepfather to the sinister forces behind it, including the Freemasons and the Illuminati. And did you know that the Queen and the entire British government, indeed the ruling elite of the world, are in fact flesh-eating green lizards from outer space conspiring to take over the globe and concealing their true identity by disguising themselves as humans? These are only a few of the conspiracy theories that are swirling around the internet, propagated through books and articles, and discussed in pubs and bars in countries all over the world. Conspiracy and Democracy, an interdisciplinary project I founded with colleagues in Cambridge, brings together historians, political theorists, philosophers, anthropologists and internet engineers to investigate this phenomenon. One and a half years into the project, we are beginning to find our way towards some answers.

Did this happen in an American desert? Some think it did. Credit:NASA Allow me to address five widespread beliefs about conspiracy theories. One, that they are a new phenomenon; two, that they are the product of the internet; three, that they belong in the realm of fantasy and are always the product of a paranoid imagination; four, that they are particularly prevalent in democracies; and lastly, that they all fundamentally follow the same patterns and structures of thought. So are they a new phenomenon? As soon as we start to look at history, we immediately have to recognise that they are not. There have always been conspiracies. Ever since human society came into being, some of its members have gathered together in secret for some illicit purpose they wish to conceal from society as a whole. Secrecy is an essential element: not only must nobody know the purpose of the conspiracy or the identity of its members, they must not even know it exists. It has to be, to borrow the categories invented by former US Defence Secretary Donald Rumsfeld, an unknown unknown. And as long as there have been conspiracies, there have been conspiracy theories. The French Revolution of 1789-94, for example, was permeated by them, from Robespierre's accusations that his enemies were conspiring with the British to overthrow the Revolution, to the so-called Great Fear, when peasants were inspired to rise up and attack landowners in the belief that there was an aristocratic plot to murder them. Before that, political life under the French monarchy was shot through with rumours about plots and machinations behind the scenes.

Even seemingly stable political systems have been prone to such beliefs. Secret societies and conspiracies, the prime minister Benjamin Disraeli lamented in 1856, ''cover Europe like a network''. ''Acting in unison with a great popular movement,'' he said, ''they may destroy society, as they did at the end of the last century.'' It was fear of a repetition of the French Revolution that inspired such paranoia. Prince Metternich, the conservative statesman of the Austrian Empire who devoted his career to trying to maintain the status quo, called the network of secret societies ''a real power, all the more dangerous as it works in the dark, undermining all parts of the social body, and depositing everywhere the seeds of a moral gangrene which is not slow to develop and increase''. Only close co-operation between the great powers of Europe, he told Tsar Alexander I in December 1820, could ward off the threat. The whole of Europe was being undermined: ''Among peoples which are sick,'' one of Metternich's allies said in 1815, ''you find conspiracies.'' Have they increased since the advent of the internet? Well: the assassination of US president John F. Kennedy in November 1963 immediately became the object of an enormous number of theories, for instance, long before the internet came into our lives. Within months of the assassination, nearly half of all Americans polled thought that Lee Harvey Oswald had not acted alone; by 1983, this proportion had risen to 80 per cent. If anything, the advent of the internet has actually reduced the prevalence of conspiracy theories about the death of the president, which, towards the end of 2013, 50 years on, were believed by 62 per cent of Americans. To come to my third point, conspiracy theories are not always or necessarily wrong. Many were no mere fantasies but had, and sometimes still have, a basis in the truth. A central part of our project looks at the relationship between theories and conspiracies. In the 1820s, secret societies did indeed proliferate. In our own time, some conspiracies about key events have turned out to be true: the destruction of New York's Twin Towers in 2001 was the result of a conspiracy within al-Qaeda; the break-in to the Democratic Party Headquarters in the Watergate Hotel in 1972 was the result of a conspiracy hatched in President Nixon's Oval Office; the bombs that went off in London on July 7, 2005, were the result of a conspiracy devised by British terrorists.

Are they, then, an inevitable product of democracy, where everyone is free to put forward an explanation of major current events? In fact, we know that conspiracy theories have also been widespread in dictatorships and authoritarian regimes. Hitler banned all political groups apart from the Nazi Party and forced all organisations, including the press and news media, to close down or be turned into Nazi organisations. This forced his critics and opponents to go underground and work conspiratorially, even if it was only to produce leaflets and pamphlets for secret distribution during the night, or merely to keep the flame of communism or socialism burning until better times came. Where open dissent and criticism are impossible, the only way to oppose the government is by forming a secret society or a conspiracy. History is littered with secret plots to overthrow democratic political systems, too, notably in the 1960s and '70s with the coups d'etat that established military regimes in many South American countries. But the very existence of a dictatorship or an authoritarian regime acts as a spur to its enemies to get together behind the scenes to overthrow it. Yet when we look back at the numerous examples in history of the assassination of leading political figures, we find that most of them have involved lone individuals, rather than groups of conspirators, even if they have been acting in the name of some wider ideology. Often it seems to many people impossible to believe this fact; hence the conspiracy theories that have followed the assassination of JFK, or around the burning down of the Reichstag on February 27, 1933. To come to the final point in my list, conspiracy theories can take on a variety of forms and structures. In order to keep the aims, purposes, methods and membership of a conspiracy secret, it is important that as few people are involved as possible. Police forces and agents of those against whom conspiracies are directed have frequently tried to infiltrate them, so conspiracies have tried to ensure the loyalty of their members by the threat of retaliation against possible traitors. The reductio ad absurdum of this is to be found in G.K. Chesterton's satirical novel The Man Who Was Thursday, where all the members of a supposed terrorist plot turn out to be police agents. In early modern Europe, and well into the 19th century, conspiracies cemented the loyalty of members through sacred oaths and initiation ceremonies; indeed, in German the term for conspiracy is Verschworung, a collective oath-taking, as is the French conjuration and its equivalents in Spanish and Italian. Whether or not the oaths were religious, they owed a great deal to the rites and initiation ceremonies through which artisan guilds and confraternities sought to bind their members to the maintenance of proper standards of craftsmanship and other essential aspects of their trade – practices parodied in the supposed ritual practices of witches' covens, another form of conspiracy widely believed in during the 16th and 17th centuries.

A lot remains to be done in researching the history, structure and dynamics of conspiracy theories, their relationship with real conspiracies, and the changes they have undergone through time. It is easy to be alarmist and suggest they are a threat to democracy and to confidence and trust in democratic political systems, but there have been relatively few times in democratic countries where this has really been the case: the McCarthy period in post-war America, which arguably reduced the possibility of democratic dissent and restricted the range of political opinions it was legitimate to express, could be said to have been one. But the mere proliferation of such theories is surely not a threat in itself. The fact that some people believe men never landed on the moon is not going to undermine the American political system or any other. And the widespread belief among Republicans that President Obama is not American is an expression rather than a cause of the divisions now affecting America's public life and political institutions. Few people in the end believe that we are ruled by alien lizards in disguise. It is only where conspiracy theories are directed at long-term trends rather than specific incidents or single observable phenomena, as in the case of global warming, that there seems to be no easily obtainable resolution to the clash of opinion. And even here, the overwhelming consensus of scientists and experts is solidly behind the conclusion that global warming is happening and is the product of man-made climate change. The debate goes on, but it is not a case of conspiracy theories threatening democracy, whatever else it might be. By themselves, such theories may reinforce political suspicion and prejudice, but they are not the origin of it. To learn more about the Conspiracy and Democracy project, visit the website conspiracyanddemocracy.org Telegraph, UK