The Four Factors
Fair use is determined by considering four factors of that use. No one factor is determinative; each factor must be considered and weighed. Usually after considering each of the four factors and weighing how much each fact of your particular situation favors or disfavors fair use, you are left with an overall sense that your use is "probably fair" or "probably not fair". Really, only the courts can offer us definitive answers.
1. Purpose and Character of the Use
How do you propose to use the work? Purposes that favor fair use include education, scholarship, research, news reporting, criticism and commentary. Non-profit purposes also favor fair use. Commercial uses weigh against fair use. The biggest mistake we see educators making is mistaking their educational context for an educational purpose. If you create a class website or presentation and put a pretty picture on it primarily for decoration or visual interest, this is very different from an image about which you are providing direct instruction.
2. Nature of the Copyrighted Work
Remembering copyright is designed to protect works of creative expression, the more highly creative the work you want to use is, the more fair use is weighed against. This is, of course, subjective. We might say, in general, a novel would be more highly creative than a work of non-fiction but, of course, there is a huge range of creativity within the huge category of "non-fiction". Unpublished works would also be less likely to qualify for a fair use than published works.
3. Portion Used
This is the one where everyone seems to want to see some percentage or number of pages that will always be fair. There is no such number. The goal of fair use is to make available a wide and unpredictable set of uses. Could a legislator predict in advance that a future satirist would never need more than ten percent of a work in order to make their point? Of course not. As a general principle: using less of a work is always more likely to be fair than using more. The smaller the portion used is relative to the whole, the more likely the use is to be fair. It is also true, however, that using an entire work can be and often is a fair use. Another guiding principle: using only the portion of a work that is absolutely necessary in order to meet the educational (or other fair) purpose you have in mind is more likely to be fair than using more than is necessary. For example, if you are considering copying a 4-page article for your class because the author makes an argument you'd like to discuss but that argument could be well understood by reading just a couple of paragraphs of the article, copying just those paragraphs would much more strongly favor fair use than copying the whole article. The more the portion you want to use represents the "heart of the work”, the less likely your use is to be fair. This can be a very difficult one to assess.
4. Effect of the Use on the Potential Market
The most useful way to think about this factor is to ask if your use could substitute for the original in the marketplace. Would your use substitute for sales either to your students or to anyone else? A confusing piece here is the permissions market. A strong market exists in selling permissions to use content, especially things like book chapters and journal articles. So, it can be easy to say "Oh, of course my student won't be subscribing to Professional Journal X so copying an article certainly doesn’t substitute in the market". But it would substitute for that secondary permissions market. We don't at this time have truly conclusive case law to guide us in thinking about the permissions market but it does seem very likely that where there is a viable permissions market for the material you want to use, this would weigh against fair use.
A Balancing Test
Once you have looked at all of the factors, you can assess if taken as a whole your use seems likely to be fair or likely to be unfair. No single factor is determinative and you could "strike out" in three categories but have the remaining category weigh so strongly in favor of fair use that, overall, your use is fair. We discuss this in more depth below in "Thinking about Fair Use: Transformativeness".
