because using a paper for two different classes is unethical for many reasons. First of all, you may be not cheating on your classmates, but you are cheating on yourself. Indeed, you are not really learning anything by not doing the work. Also, doing self-plagiarism is being dishonest with your teacher. When a teacher gives a grade, it is based on the student’s understanding of the course and on the effort he puts in the paper. He is showing neither of those two by resubmitting a paper from another course. Finally, it is a certainty that, if this student would do the paper as asked, he would not write the same sentences and ideas as on his previous paper and therefore would not get the same grade. Maybe it would be greater, maybe it would be less. The point is that it would (probably) not be the same grade. For all these reasons, using the same work twice is unethical