Why Are Introductory Classes Called "101"? [closed]

The 101 course code used to be ubiquitous in reference to the first level of any subject for which other levels existed. The 3-digit form was standard in the quarter system (in which three quarters = one academic year, saving the fourth "quarter" technically to refer to the summer). In this system, a 100-level code refers to a freshman-level course, a 400-level one refers to senior year, 500 is for master's programs, and higher numbers are for Ed.S., J.D., M.D., and research-based doctoral programs (Ph.D.). On this basis, the tradition was to make 101 the first foundational course in a series of courses of the same subject area at the freshman level. By comparison, the semester system typically uses a 4-digit course code (e.g., 1101). Over time, course numbering has become more arbitrary. For example, you can now find quarter systems with numbering like 1A, 1B, 1C, and so forth (instead of 101, 102, 103), and many universities now also start with 100. This arbitrariness probably stems from program restructuring using legacy course codes: Changes in course numbering are both confusing for students who are trying to meet their particular catalog's requirements year after year (when numbering might be changing) and hard to implement in electronic databases.