There are three kinds of live sources: actors, commentators, and pathfinders. Stories consist of actions performed in time for reasons by actors. So for greatest effect, we try to use the actors themselves as primary sources of information; they were there. The commentators frame the situations and issues surrounding the action; they tell what it means. So what’s a pathfinder?
Pathfinders know things without being involved. If you find them early, gathering gets lot easier. We ask them to lay out the ground for us, identify the actors and commentators, and help gain access to them. Writers flatter pathfinders by asking their advice, and reward them by not mentioning their names or quoting them. Thus pathfinders can affect events without risking involvement or disclosure.
Suppose you’re writing about a new kind of stent used in heart surgery. Your pathfinder might be a cardiologist who knows all about stents but doesn’t implant them. She could tell you how stents work and how this stent will work, who are the players involved, the likelihood of success and problems, and the names of experts who can comment on the record. If you’re really lucky, she closes the conversation by telling you to drop her name so sources will talk to you. When you write the piece, you don’t quote her or mention her, but you send her a copy with your thanks.
Today’s source, properly treated, may become next month’s pathfinder, and vice versa. Smart writers develop a bevy of pathfinders for different subjects, and always call them first. They save time, false starts, and errors.
http://www.public.iastate.edu/~honeyl/Rhetoric/