‘PR is the discipline that works to align what others think of you with what you think of yourself and seeks to elevate both.’
We both teach the subject (Chris is programme leader for public relations at Lincoln University) and see the virtue of a simple, memorable metaphor for teaching purposes. I think it also serves to elevate the significance of internal communications in the equation.
What no definition can or should do is say how the PR practitioner sets about achieving this balancing act. This is more than a question of tools: it’s about ethos. While the marketer works with products and brands, I view the PR practitioner as engaged in a battle for ideas. How to establish company X as the best place to work in its sector; how to make campaign Y succeed; how to ensure company Z remains trusted. Where there are ideas, there are abstractions, and this is what makes public relations challenging to teach (and, sometimes, difficult to learn).
PR Studies 
Note this list (via Corporate Engagement http://trevorcook.typepad.com/weblog/2006/06/how_we_see_ours.html) of the traits of the successful practitioner:
‘Good written and oral communication. Good research and analytical skills. Ability to see things from the other perspective. Knowing what’s newsworthy. Public relations experiences, particularly in stakeholder consultation and issues management. Ability to understand context and environment. Applying logic and sophisticated analysis to complex situations. Lateral and strategic thinking. Providing a strategic perspective to management. Providing advice to produce business results and further the corporate mission. Having the confidence to make decisions under pressure.’
I liked very much the observation about the need of the methafor, and the lack of the substance in the definition (at least that’s how I saw it).
Still, I wouldn’t insist so much on the role of the ideas (it makes it sound too philosophical), but rather on the importance of strategy.
If marketing is a war, than PR should be the strategic thinking behind it.
Perhaps ‘elevate’ invites too great an aspiration. I believe that we seek convergence which has sociological, psychological and neuro-psychological underpinning. It also works for most domains of PR practice including relationship management.