From Pope Urban II's call for a Crusade to reclaim the Holy Land to the speeches of Adolf Hitler, George W. Bush and Tony Blair, "incendiary rhetoric is one of the motivating factors in civilisation".

That argument was made by Nicholas O'Shaughnessy, professor of communications at Queen Mary, University of London, who was due to give a lecture on "The Abuse of Rhetoric" this week.

Professor O'Shaughnessy was set to draw parallels between the German invasion of Poland in 1939 and the invasion of Iraq in 2003 at his inaugural lecture, to be held on 10 March at Queen Mary's Mile End campus in London.

"Both were sold as legitimate self-defence on a bogus prospectus to people who didn't want to go to war," he said.

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"When we listened to Blair's speeches, those of us who were historically informed felt that we'd seen it all before."

Professor O'Shaughnessy called for "the renewal of interest in rhetoric both as a public and an academic study".

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The topic is now rarely studied as a separate academic discipline in the UK, but he argued that "rhetoric is not a trivial instrument or a decorative motif in history". On several occasions it has even acted as "the amanuensis of genocide".

The power of words is evident everywhere: when opponents of abortion packaged their cause as a "right to life", or critics of genetically modified crops called them "Frankenstein foods", they "sabotaged all rational public discourse in the area", Professor O'Shaughnessy said.

But although all regimes make use of slogans and soundbites, a few have been so dominated by their own rhetoric that it becomes "the core political competence of government", driving their policymaking and blinding them to reality.

"What the Nazis did more than anything was use rhetoric," the professor observed. "They were decades ahead of parties in other countries, for example in their use of direct mail. Hitler became the overall editor of public communications in the Third Reich. Communications was not an instrument but the medium they swam in."

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Such techniques, however, inevitably fail in the long run, he said.

"Hitler believed that propaganda was everything. He saw it as a magic panacea for gaining and holding on to power - and yet it proved the source of his defeat. He was so determined to win a symbolic victory at Stalingrad that it led to disaster."

Despite the moral differences - Professor O'Shaughnessy sees Mr Blair as "an utterly naive, misguided idealist, a victim of his own rhetoric" - New Labour has been undermined by similar flaws, he suggested.

"Rhetoric allows politicians to be evasive, to avoid direct responsibility for the consequences of action by surrounding everything with a skein of vagueness, such as the phrase 'tough on crime, tough on the causes of crime'.

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"One of the most memorable features of the Iraq War was its rhetoric. This was a conflict surrounded by a miasma of words, a penumbra of slogans, a verbal stew of 'coalitions of the willing', 'shock and awe', 'collateral damage', 'Operation Iraqi Freedom', 'regime change', 'effects-based warfare'; the list is a very long one indeed."

Professor O'Shaughnessy added: "All of this was designed to frustrate clear thinking about the war, and to a considerable extent it succeeded."

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matthew.reisz@tsleducation.com.