Two men are running for mayor of your city:

• Candidate One is a respected local doctor who runs a clinic providing free treatment to the families of local unemployed mill workers. He's been a tireless member of the local secondary school board, including five years as its president during which enrolments soared. Then there's his Congressional Medal of Honor, which he won as a medic in the first Iraq War by exposing himself to enemy fire to treat wounded infantrymen in no man's land. He's happily married and without a hint of personal or financial scandal. In fact, apart from reminding you that you're less than perfect by comparison, he has only one negative. He is the most boring speaker you have ever heard. As he moves ponderously through his now familiar stump speech, you find yourself losing interest in his policy ideas even though you've wished for them your whole life.

• Candidate Two is an amazing public speaker. He has the ability to electrify the huge crowds that pack the local town hall, employing rhetoric that moves you alternatively from tears of pity to fist-waving rage, and although you once opposed his policies, you find yourself joining in his refrain: ‘Just do it’. Perhaps he's the agent of change the city really needs. But as you leave his rallies, you can't help but remember that unfortunate night he was arrested in a hotel room with that 15-year-old girl, and how at the trial the girl and her parents stunned the prosecution with their last-minute refusal to testify. Now, on the eve of the election, the local paper is reporting that the girl's outraged grandfather believes the parents were bribed by the candidate's attorney.

If, like most people, you end up voting for Candidate One, you've understood a crucial element of oratory: the character of the speaker – or what the Greeks called ethos. No amount of charm or logic will persuade the reasonable listener if the speaker is a known liar or suspected phoney or hasn't the strength of purpose to deliver what he or she promises.