A speaker makes two kinds of promises to an audience – the explicit and the implicit.  Explicit promises involve foreshadowing, framing, and creating signposts in your talk (by the end of the talk, you’ll know how to charm sparrows from trees and have them eating out of your hand; there are five ways to prevent early hair loss; that child never saw its parents again).  Implicit promises center on the premise of a speech:  that you, the speaker will deliver something worthwhile and possibly life-changing; that you will know what you’re talking about; that you won’t sell too much from the stage.

You have considerable scope to play with the first set of promises; you should not break the second set, the implicit ones.

Listening to a speech is hard work, and audiences need all the help they can get.  The ear is an inefficient recorder.  The mind quickly gets overwhelmed.  By the time you’ve listed four of the five ways to prevent early hair loss, the audience is forgetting the first one in its desperate attempt to remember the fifth.

So it’s really important to provide promises – those signposts – to help the audience through its listening work.  Let it know, at a very high level, what the arc of the talk is.  You don’t need to provide an agenda slide, but you do need to hint at the structure:  that’s what I want to talk to you about today – how to gut a fish.  You also need to tell the audience why the talk is important:  because you never know when you’ll be thrown out of an airplane into the Alaskan wild and have to subsist on fish you catch from a stream until the search parties find you and that may take a long time because the cell phone coverage is so spotty out there.

Then provide lots of signposts along the way to help an audience keep track of where you and they are:  I’ve got three more kinds of tooth decay to talk about before we move on to peritonitis.  And give the audience local signs about where they are in a sentence or a paragraph:  on the one hand, you have large-billed toucans; and on the other hand you have the small-billed variety.  That sort of hierarchy helps the audience make sense of a sentence just as the three kinds of tooth decay help the audience make sense of a section of the speech.  It’s better than saying, you have large-billed toucans and small-billed ones.  Don’t give the audience undifferentiated lists; rather, give them comparisons, hierarchies, evaluations, and spectrums.

The implicit promises, on the other hand, must never be broken.  Speakers today need to be authentic, and real, and not too sales-y.  They need to be expert enough to cover the topic at the appropriate depth for that audience.  If your topic is physics, for example, one kind of expertise is needed to talk to a high-school audience and another to talk to grad students majoring in the subject.

The more explicit promises you make and keep, the happier your audience will be.  The fact that you fulfill the implicit ones will simply keep you out of trouble and allow you to connect with an audience and deliver something of value.  Implicit promises are — or should be — a given.