Judging whether a use is "fair" is hard. This is because none of these factors are absolute; all of the factors function on a continuous sliding scale, and the only time a firm answer is provided is after the factors have been considered by a court of law.
Note: Parodies which have disrespected established wholesome iconography have fared poorly under the "fair use doctrine." Courts have ruled that use of these works is not considered to be a “fair use” despite meeting all the requirements associated with “fair use.”
The purpose and context in which a work is reused is one of the factors considered to determine if the use of a work is "fair use." Transformative nonprofit uses including using a work for education, research, scholarship, or instruction are considered to be fair. Using a work for other commercial purposes (i.e. to advertise a product) are considered "less fair."
Some types of works receive a higher level of copyright protection than other types of works. For instance, works of fiction receive a higher level of protection than works of non-fiction. This is because works of fiction require a higher level of creativity and these works can be judged as being more unique. For example. J. K. Rowling's writings about the fictional location of Hogwarts will receive a high level of copyright protection than a non-fictional account of the TTUHSCEP campus.
Another factor that needs to be considered is the amount of the original work that was used. Did you use the entire work? Or did you only use a small portion of the original work? Sometimes even using only a small part is unacceptable. This happens when the copier inadvertently selects material, which embodies the "heart" or the "essence of the work." In the case of the Shakespearean play "Hamlet," the "To Be, Or Not to Be" soliloquy would be considered the heart of the work because it sums up Hamlet's experiences during the course of the play. So just using the soliloquy would be unacceptable if this work were protected by copyright (all of Shakespeare's play are currently in the public domain).
The effect of using the work on the current and future commercial market for the work is the last factor that needs to be considered. This means that if using the work hurts the current and/or future sales of the work the use is not "fair." A use may meet all the other criteria, but be unfair because it fails this last test. For example, if a teacher copies a single chapter from a non-fiction textbook to use in class, and thus causes the textbook's authors to lose sales of the textbook to the 40 students in the class, the use would not meet the criteria for a "fair use."
There are three tests which have been traditionally needed to be passed in order to allow for the "fair use" of copyrighted printed materials in the classroom. These are the Brevity Test, the Spontaneity Test, and the Cumulative Effect Test. All three tests need to be passed in order to claim "fair use."
Brevity Test involves the amount of material used from a work. It states that the use of copyrighted material needs to be as small as possible. This limitation involving the character of the use sets specific limits to the amount of information from a single work, which may be used.
Spontaneity Test involves the source of the inspiration for the use, and how much time has passed between the decision to use the work and when the work was used. To pass this test both of the factors must be met.
Cumulative Effect Test deals with the effect of the use on the market and the profit realized by the author of the work. It is meant to limit the commercial impact of the use and includes: