"I'm sure I read somewhere that 10% of a work is always fair!"
"Isn't it okay if I use something one term but then I have to get permission the next term?"
We know from looking at the four factors of fair use that no specific amounts are dictated and there's nothing in there about 'spontaneity' or 'cumulative effect' (all that "one term free" business). So why do so many of us remember hearing these things somewhere along the line? These concepts come out of the Classroom Guidelines. These are a set of negotiated guidelines agreed to by the Association of American Publishers and The Author's League of America following the passage of the 1976 copyright law (which first codified fair use). The Guidelines are an agreement between private parties intended to provide a kind of "safe harbor," that is, the publishers were essentially saying that the guidelines represent, in their opinion, an interpretation of the minimum standards of fair use that they could live with and if educators operated within that "safe harbor" they would not be liable for infringement. The guidelines specifically state that they are meant "to state the minimum and not the maximum standards of fair use under section 107". Despite this, many groups including the American Association of University Professors (AAUP) objected to the Guidelines as they feared they would come to be seen as, in essence, a ceiling rather than a floor. That is, to express the limits of fair use rather than the minimum. This fear has most certainly proven to be well-founded with many institutions enshrining the Guidelines as policy. Certainly the Guidelines are widely conflated with the actual law.
The Guidelines can be helpful, especially when regarded as the "floor" they were intended to be. Remember that there is no real guarantee that the Guidelines do actually represent a "safe harbor" as they do not carry the force of law. But, more importantly, remember that the very nature of fair use is that it does not attempt to anticipate all future potential uses and describes in advance if those uses are fair.
