And "To whom are they speaking"?

What you are giving a succinct overview of is Aristotle's _Ars Rhetorica_ Cracking read, BTW.

Yes indeed I had neglected the "To whom"...which reminds me how often I think a message is aimed at me (egomania) when in fact it has an audience I am not even aware exists...

Is there a good translation available somewhere?

Follow the money. If you can't see a person's motivations (esp. a politician), watch the result of their actions and assume that the outcome was their motivation and tell them that. Practically it doesn't matter whether they intended for that outcome to occur or not, because you still have to bear the consequences. If they predict the undesirable outcome, they should alter their behaviour. If the same behaviour repeatedly maps to the same outcome regardless of who is doing it, judge the person on the outcome. Drunk driving laws work like this.

My introduction to this were the excellent books 1421, 1434, and of course, the author's third book, The Lost Empire of Atlantis, which I found every bit as convincing as the first two and really drove home how credulous I'd been when reading them.