Many courses at NHTI are dependent on knowledge learned in preceding courses. NHTI requires students to pass all listed prerequisite courses to proceed with courses for which there are prerequisites. Prerequisite courses may be waived only with the prior approval of the department chair in which they are taught. Such a waiver does not suggest these prerequisite courses need not be taken, only that credit for them may be gained at a subsequent time. Corequisite courses are those that must be taken concurrently (at the same time) with another course, as listed in a particular course description. With departmental permission, a corequisite course may sometimes be taken in advance of the course for which it is a corequisite.