In certain subjects, such as the sciences, mathematics, and the foreign languages, courses (particularly at the introductory or intermediate level) must be taken in sequence because the concepts introduced and skills acquired at one level are needed for successful work at the next higher level.
Once a student has successfully completed a course at a higher level in a sequence, the student may not subsequently enroll in a course at a lower level in that sequence. For example, you cannot take Math 105L after having successfully completed Math 111L or Math 111L after Math 112L. Similarly, Spanish 101 or 102 may not be taken after Spanish 203.
Advanced courses generally do not stand in sequential relationship to one another, unless otherwise indicated. For example, advanced (300-level) language courses may be taken for credit without regard to their course number.