The doctrine of fair use was not originally a part of copyright law, but developed slowly through a number of court decisions. It is now an official part of the copyright law as enacted by legislation. Basically, it sets the parameters as to what use other people can make of a copyrighted work before they must secure permission (or risk infringing the copyright).
Unfortunately, the lines drawn by the doctrine of fair use are not always that clear. There is no set number of words, or percentage, or any other clearly delineated factor. Rather, it has to be a subjective analysis based on the use to which the copyrighted work is put.
The following bulleted list is culled from the 1961
Quotation of excerpts in a review or criticism for purposes of illustration or comment.
Quotation of short passages in a scholarly or technical work, for illustration or clarification of the author's observations.
Use in a parody of some of the content of the work parodied.
Summary of an address or article, with brief quotations, in a news report.
Reproduction by a library of a portion of a work to replace part of a damaged copy.
Reproduction by a teacher or student of a small part of a work to illustrate a lesson.
Reproduction of a work in legislative or judicial proceedings or reports; incidental and fortuitous reproduction, in a newsreel or broadcast, of a work located in the scene of an event being reported.
The doctrine of fair use, then, tries to strike a balance between the copyright owner's interests and the interests of society at large to benefit by additional information being produced. To determine the scope of the doctrine of fair use, section 107 of the Copyright Act sets out four criteria to consider:
The purpose and nature of the use of the copyrighted material. Is the reproduction being used for a commercial use? Is it for nonprofit or educational uses? Is it being used for scientific research? Is it being used for the purposes of criticism or commentary? All of these questions shed light on the analysis of the first point. The more commercial the use is, the less likely the use will be considered to be “fair” for the purposes of the doctrine of fair use. Uses such as teaching and research are given more breadth. The nature of criticism and commentary usually requires that a portion of the work being considered be quoted to some extent; as long as the reproduction isn't too substantial in the context of the criticism, the use should be considered fair, too.
The nature of the copyrighted work. Is the work being reproduced merely factual in nature? Or is it something that came from the imagination of the author? Is it something that was written for the betterment of society, or is it purely entertaining in form? Is it something that was written specifically for commercial exploitation? The nature of the work that is being produced is as important as the use to which it will be put.
The amount of the work reproduced, relative to the copyrighted workas a whole. Reproducing one or two lines of a poem or a song may be acceptable, while reproducing the whole thing will probably be seen as an infringement. What is important is how much of the work is being reproduced. If the answer is “most,” then you're probably on your way to infringement, and you should either find another way of doing things or start seeking permission from the copyright owner. In the professional world, obtaining permission is sometimes referred to as “clearance.” Either way, it's always a good idea to get permission if you're using a poem or a song, since even one line can be a very substantial portion of such a work. With other types of work, a paragraph or two is probably okay. What is important, again, is the relationship between the work you are reproducing and the original work as a whole. Condensing the original work into a précis (a condensed, summarized form of the original work) will probably be an infringement, because you are reproducing a substantial part.
The potential market impact and how it may affect the copyrighted work. If a work is out of print and not commercially available, reproduction of a part of it (even a relatively substantial part, depending on the circumstances) will probably be considered fair. If the owner of the copyright is in a position to charge a fee for the use of the material, this tips the balance out of the realm of fair use, but this also must be considered alongside the other factors. If a work is commercially available, your use may replace the need for a consumer to purchase the original work, and therefore any reproduction you attempt will probably not be considered fair.
Of course, the doctrine of fair use merely allows you to use the material without first seeking permission. If, after considering the factors outlined above, you decide that your proposed use would not fall within the fair use doctrine, you can always contact the copyright owner to obtain permission. In some cases, the payment of fees is required; however, a great number of authors are happy to see that their works are being cited and readily grant permission.
If you are concerned about a particular use and whether or not it will be considered fair, it may be best to consult an attorney for a legal opinion determined with regard to the particular facts.
When to Use Citations
Copyright and plagiarism are related concepts, but they come from completely different backgrounds. Copyright exists primarily to benefit the copyright owner economically. Plagiarism, on the other hand, is not a legal concept; it is entirely a moral concept, outside the purview of the law. However, it can still have serious repercussions. Many academic institutions, such as colleges and universities, treat plagiarism with the utmost severity, even permanently expelling students for violations. Don't risk it — use citations where appropriate.
Quoting or Referring to Experts
Because copyright protection does not extend to the ideas expressed in the work, you can safely state the ideas and conclusions of others without regard to existing copyright. Copyright cannot be used as a monopoly for an idea, so these types of quotes can be used as long as the usage does not infringe upon the copyright of another. It's still good form, however, to quote your source.
If you are not writing an academic paper, merely acknowledging the source should be sufficient, as in the following example:
According to Professor Bloggs of the University of Arkansonia's literary studies department, 37 percent of male teenagers like to read spy novels, while only 12 percent of the adult male population likes to read them.