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. A commercial duplication of an article from a journal might weigh 5 against fair use. But a commercial commentary, while still weighing against fair use because it's commercial, would only weigh about 2 or1. 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.
Again, uses on the left tip the balance in favor of fair use. Uses on the right tip the balance in favor of seeking permission. But here, uses in the middle tend to have little effect on the balance. Small amount More than a small amount This factor has its own peculiarities. A nonprofit use of a whole work will weigh somewhat against fair use.