Courses numbered 1 through 99 are lower-division courses and are normally open to freshmen and sophomores. Courses numbered 87 are Freshman Seminars. Courses numbered 100 through 199 are upper-division courses and are ordinarily open only to students who have completed at least one lower-division course in the given subject, or six quarters of college work. Courses numbered 200 through 299 are graduate courses and are ordinarily open only to students who have completed at least eighteen upper-division units basic to the subject matter of the course. Courses numbered 300 through 399 are professional courses for teachers, which are specifically designed for teachers or prospective teachers. Courses numbered 400 through 499 are other professional courses.