You Talkin' To Me?, By Sam Leith

Politics is pursued through rhetoric, which makes rhetoric just about the mightiest force on earth. Barack Obama is the contemporary case in point, because it is his rhetorical prowess that has made him the most important person around. Sam Leith analysed Obama's oratory for a newspaper feature before becoming fascinated by the broader territory of rhetoric, and this book is the result.

Rhetoric's first great theoretician was that incorrigible classifier, Aristotle, who laid out its main branches. But the great classical practitioner was Cicero. Undaunted by possession of a name that means "chickpea", he honed his fearsome talent in the law courts. His first major case was a parricide. More eminent lawyers turned down the brief, wary of the taint of this most heinous of crimes, so abhorred that perpetrators were beaten cruelly before being heaved into a river or the sea inside a leather sack that also contained a dog, a cock, a viper and an ape. Cicero triumphed. He cleared the defendant, before going on to trounce his accusers (Roman legal proceedings differed rather from our own), thence romping off to fame and fortune.

During Leith's tour of other epic speakers, the section on Churchill is engrossing. For much of his career his orotund approach did not find favour and it was only with the advent of war that his grandiloquence became attuned to the times (though still mocked for excess ham).

But Leith is disappointing on Hitler. The Führer always started slowly and ominously before accelerating into ranting, yet there's a lot more to explain. How did his hysteria so mesmerise his listeners and gain their joyful assent to his dark agenda?

When it comes to Obama, Leith's scrutiny is painstaking and he is especially illuminating on Obama's debts to Abraham Lincoln and Martin Luther King. Obama's signature rhetorical figure, it transpires, is "anaphora", or the repetition of words or a phrase at the beginning of a clause or sentence - although his monumental "Yes we can" was its opposite, or "epistrophe".

Leith's style is blokey and jokey, illustrating one point here with an anecdote about a friend buying a castle surreptitiously, underlining another there with an exchange from The Simpsons. The result is an entertaining primer, yet it stands as a reminder that rhetoric is much too important for the common good. That's because of the fundamental disconnect of politics: rhetorical talent has no necessary connection to executive ability.

Obama is sadly relevant here too. Post-election, his verbal wattage has diminished, since passionate oratory is useless for rescuing his country's finances. As for the future of rhetoric itself, the best speeches are always remembered though brief quotations, but broadcast and social media continue to make soundbites ever more crucial. If Cicero was still with us, no doubt he'd be Tweeting away furiously about ongoing debasement of the noble art. "O tempora o mores ..."