Plagiarism and copyright infringement are distinct but not mutually exclusive. Both can happen unconsciously. Plagiarism means failing to explicitly indicate w

Plagiarism and copyright infringement are distinct but not mutually exclusive. Both can happen unconsciously. Plagiarism means failing to explicitly indicate which author you copied which ideas/expression from. You can plagiarise regardless of whether the author gave you permission to copy. To my knowledge, the US doesn't have laws against plagiarism per se. (The US does have laws against academic dishonesty, fraud, and copyright infringement.) Copyright infringement means copying/modifying a rightsholder's copyrighted expression 1. without a license from the rightsholder or 2. in a way which violates a condition of the license you got from the rightsholder to copy/modify the expression. Both of those scenarios are subject to fair use in court, considering that the second scenario effectively is a case of the first scenario. A copyright license may require you to provide attribution in a specific manner; failing to comply would revoke your license permanently or until you comply (depending on what the license/rightsholders say).