At Saatchis, it was a Single-Minded Proposition. And it was all about focus down to the brutally simple, which would then inspire the creatives to great things.
In these days of Web 2.0, it's not so easy. Or simple. We're not just about messages any more. We're not in the world of "what our advertising should say", because we're not just interested in what our communications "say", we're interested in what people pick up and what they do with it.
I don't work in an agency at the moment, but I can imagine there's been a lot of wringing of hands about what to call that pivotal part of the brief. Is it a "start point" or "conversation catalyst"? It's a thought, yes, definitely a thought - but is that "thought" disruptive or merely "central" or "key" somehow? Or is it a "brand truth" or "emotional connection"?
Whatever we call it, never mind what used to be called the "target audience" - what exactly do we expect or want the creatives to do with this thing once we've given it a label? All of this can lead us into areas of vague and wooly thinking - I know, because I've been there.
I don't have the Archimedes-style answer, maybe because there isn't one. I'd certainly be interested in any other views and experiences on this. In the meantime, I'll try my best to hang on to those past ways of thinking that still make sense with one hand while grasping the changes in the ways that brand communications work in the other.