I once called on a politician campaigning to run his country, having earlier attended one of his rallies in order to watch a speech connoisseur at work. We happily interrupted our work discussion to dissect the intricate, interlocking components of his speeches. We talked about use of cadence and repetition; the building of rhythms; how he showed he could make and take a joke; where he started to build to a climax; why he used English phrases now and again; and what part gestures played in the repertoire. We paused reluctantly when the political schedule dictated his departure for yet another rally.

In Australia, such an exchange would be distinctly unlikely. We are too casual about the quality of speeches, let alone speech writers. I asked one prime minister about the message he wanted to convey in a speech, only to have him reply: "how do I know what I think until I see what I say?" Another simply read out texts I supplied, leading me to believe he was either focused elsewhere or that we enjoyed an uncanny empathy. (The first option was preferable - and plausible.) A deputy prime minister created much more fun. He would deliver a speech as written, but interjecting riffs, anecdotes and asides. They took as long again but were twice as entertaining.

Other countries also tell tales about their leaders' speeches. Gerald Ford's advisers included a stage note in a speech, only to have the president insist out loud that something should be done - "with emphasis". John Kennedy followed up a stirring sentence by confusing the inhabitants of Berlin with a local jam doughnut. Egyptians used to allege that President Mubarak had demanded a 10-minute speech, then taken half an hour to deliver the address. Furious, he rebuked his staff before they pointed out that he had been handed a ten-minute speech, just three copies of it. One French politician was reminded that, with his speeches as with his campaign book, one was supposed at least to read the pages before claiming them as your own work. Even the best star speechwriter, Peggy Noonan, would have despaired.

I used to assure colleagues suffering speech stage fright that all they had to do was think clearly, have something to say, then find a clear, simple way to make that point. Other forms of writing are less public but demand more. The Irish author Colum McCann insisted to me that writing a novel entailed going out into the world to discover a story which broke your heart, then working out a way to recount the tale which would break a reader's heart as well.

Now I would add to the mix one exacting condition. No pandering would be involved. Although you do need to have the politicians' voice in your head, that does not mean always obliging them. Politicians' demand of speechwriters is usually, as Willie Nelson puts it, to "lift us up where we belong, where the eagles fly". In fact, few can fly.

Nor is pure originality necessary. Speech writers are scroungers, plagiarists, cannibals. Rather than standing on the shoulders of their more illustrious predecessors, wordsmiths devour the substance of those who have written before. No decent writer of speeches in the past 80 years has not feasted on Winston Churchill's 1940 speeches, learning about structure as well as passion, cumulative effects in addition to one-liners.

Nor should a good speech be stuffed with substance, like a hot cross bun with raisins. An oratorical box of AllSorts is merely muddle. To paraphrase two Tasmanian pie advertisements, the writer does have to supply "meat you can eat". She should not, however, pack in so many facts so that "you meet the meat first bite".

Speeches which last can be drafted from left or right, in peace or war, now or two millennia ago. The pre-requisite for durability is that the text demonstrate moral clarity and serve a moral purpose. A great speech needs to account for things worth fighting for. That is why there are so few.

2451 years ago, Pericles reminded Athenians they should willingly die in battle because of the glories of their democratic system and city: "For the whole earth is the graveyard of brave men."

Abraham Lincoln crafted at Gettysburg a compelling argument for "government of the people, by the people, for the people".

Franklin Roosevelt claimed - in a pretence converted into hope - that "the only thing we have to fear is fear itself - nameless, unreasoning, unjustified fear".

John Curtin told us to "look to America", "free of any inhibitions".

Paul Keating forced white Australians to confront guilt and shame at Redfern. "It was we who did the dis-possessing."

Leaving the best until last, any putative wordsmith should learn from an August 1963 address in which every sentence is suffused with moral clarity and informed by moral purpose.

"This is no time to engage in the luxury of cooling off or take the tranquilising drug of gradualism."

Driven by "the fierce urgency of now", Martin Luther King's account of his five dreams is a classic - and should never become just a cliché.

People parrot cliches without thinking. By contrast, these seven examples of clarity and purpose provide teaching moments, on how speeches might be crafted and why they matter.

We should vault onto those shoulders, and try to emulate their clear moral purpose.