Fair Use is a flexible exemption to copyright that balances the author's need to make money with society's need for knowledge to be shared and reused.
Not all educational uses are Fair Use.
Fair Use is determined by weighing four separate factors and looking at the combined outcome of all four. All four don't have to be favorable, but as a whole, they should be more favorable than not. In other words, you can flunk one factor and ace the other three, and it still might be fair use. Or you could do so-so on all four, and it could still be fair use.
A few things are always considered Fair Use:
If a work is transformative enough, it is a Fair Use, because of the unique way it fulfills the criteria of the first and fourth factors.
A Transformative Work is not a derivative work, although it might have started out that way. But instead of being a new spin on the original, or the original with something added, taken away, or changed, a Transformative Work is something entirely new that just uses elements from the original. It repurposes, recontextualizes and/or changes the work from which it borrows.
Transformative Works pass the Fair Use first factor test (nature and character of the use) with flying colors. That is because a Transformative Work creates new ideas and knowledge, which the courts consider socially beneficial enough to fall under the Constitutional phrase, "to promote progress of science and the useful arts."
Transformative Works pass the fourth factor test (market effect) equally well. That is because a Transformative Work is something entirely new that can't serve as a market substitution for the original work.
Examples of Transformative Works that have been accepted by the courts as Fair Use:
Text materials aren't covered by Educational Use or the TEACH Act, so readings that are not linked to or used with a license will have to be used under Fair Use.
Whenever possible, link to content where it "lives." Linking is always a Fair Use.
When we talk about embedding PDFs or other text files, we always mean embedding them in a course in the LMS. None of this advice should be taken to apply to blogs, websites, email, or message boards. Unlike those, the LMS has access protections that minimize market effect, and increase the case for Fair Use.
There is no clearly defined "safe amount." Both law and precedent indicate that copying brief passages for educational and scholarly use without permission is definitely Fair Use. It is also clear from precedent that copying multiple chapters of a book or multiple articles from a journal is definitely not Fair Use. A reasonable guideline is that within the LMS, a single article from a journal (not an issue, the whole journal) or a single chapter from a book is legitimate under both the spirit and letter of Fair Use. It would be risky to use any more than that under Fair Use, and we also understand if a course owner wishes to use less than that.
The course owner is the one who could be liable if the university receives a takedown notice, and they (the course owner) do not comply with it. Since the risk is theirs, the tradeoff between being cautious about copyright and being able to use content is theirs to make.