Introduction
For most of the history of our received civil procedure, a person who stood wholly outside a dispute, who had done no wrong and owed no duty, could not be drawn into a separate action brought solely to extract information from him. This was the mere witness rule: information could not be obtained by discovery from one who would in due course be compelled to give that same evidence as a witness at trial.1
Discovery was auxiliary, dependent on an existing cause of action, and no freestanding suit lay merely to gather evidence or unmask a wrongdoer from a stranger to the controversy.
The rule answered two main concerns: preventing harassment and preserving the structure of litigation. The first, allowing any person with a tangential link to an issue to be sued or examined merely because he might know something useful would license oppressive fishing expeditions against innocent bystanders. The second, preserving the ordinary architecture of litigation, in which