If Jon must enroll in Economics 101 or Political Science 101 this semester, how could I make a reasonable assumption that he can also register for both? There's no context in the sentence that indicates that. Especially with the topic of registering for courses, the given sentence really indicates that both are sufficient to fulfill some requirement because he can take either course. So again, why would I assume this is and/or. It just doesn't seem like a logical assumption to make grammatically.