where there is no "substantial adverse effect, financial or otherwise, on the exploitation ... of the existing work ... or on an existing or potential market for it, including that the new work or other subject matter is not a substitute for the existing one".
"solely for non-commercial purposes"
Culture is interdependence, and requiring each act of deliberate dependency to render an accounting would destroy the synergy on which cultural life rests. Even if the accounting were done painlessly — by a magic computer that somehow could costlessly determine who contributed what and could prepare a continuously up-to-date, self-executing list of debits and credits — part of our self-concept as a people depends upon our having a common heritage. Parceling out that heritage to only those willing and able to pay destroys part of its value. Wendy Gordon, On Owning Information (1992)