Fair use grants the right to utilize works protected by copyright without the need to receive permission from a copyright holder. Four factors are integral to consider if the use of a work is eligible:
Factor 1: Purpose of the work's usage
If the protected work is to be used for non-profit, educational or personal reasons, it is eligible for fair use. Portraying the work as criticism, commentary, news reporting, teaching, scholarship, and/or research strengthens the argument for non-profit, educational or personal reasons.
Works to be used for commercial, entertainment or for-profit use are generally not eligible for fair use.
Factor 2: Nature of the work's presentation
Works consisting more of factual information (rather than creative material) are more likely to be eligible for fair use. Published work is also likely to be eligible for fair use, provided that the original author is given credit for creating the work.
If the work is unpublished or largely fictional, it is likely that permission is needed from the copyright holder.
Factor 3: Amount of work utilized
While there is no scientific formula to measure this, a small amount of work (for example, a paragraph from a novel) is more likely to receive fair use than several chapters. It is also important to consider how much the borrowed material means to a fair use presentation. The more central it is to the presentation, the more likely you will need permission from the copyright holder to use it.
Factor 4: Market effect
Fair use is likely to be granted if the use of protected work will not influence the public market. As a general rule, the more restricted the use of the work, the less of an impact it will have.
For example, fair use would be much more likely granted to a person wishing to present protected material to a classroom of students, rather than as part of a public broadcast that could reach a much larger audience.
One can claim any or all of these factors in an attempt to use protected material via fair use. It is always best to carefully consider and assess the risk each time you intend to claim fair use, as misrepresenting or otherwise incorrectly using protected works could violate STLCC Copyright Policy as well as result in lawsuits from copyright holders.