Factor 1: Character
Question: What is the character of the use?
The use on the right tends to tip the balance in favor of the copyright owner - in favor of seeking permission. The uses in the middle, if they apply add weight to the tipping force of uses on the left; they subtract weight from the tipping force of a use on the right.
Imagine that you could assign a numerical weight to each use. A nonprofit educational use other than the middle uses, for example, making a copy of a journal article for a university class, might weigh 5 in favor of fair use. But a nonprofit educational use that is also criticism, for example, the inclusion by a faculty member of a quote from another's work in a scholarly critique, would weigh even more in favor of fair use: about 6 or 7. That's because the uses in the middle are "core" fair uses; the ones most dearly protected.
Even if they are for-profit, the core fair uses weigh in favor of fair use: that's why they subtract from the weight against fair use of a commercial use. A commercial duplication of an article from a journal might weigh 5 against fair use. But a commercial commentary or quotation would barely tip the scale, if at all.
This is not to suggest that fair use can be precisely quantitatively analyzed. Numbers are just a tool to illustrate how the facts interact and affect each other. Actually, numbers wouldn't make the analysis any easier: copyright owners and users would have just as much trouble agreeing on weights as we have agreeing on any other judgment about fair use.
Think about the uses you would need for teaching and research. Do they tend to weigh in favor of, or against fair use?