" The ordering of knowledge has changed with the centuries. All knowledge was once ordered in relation to the seven liberal arts— grammar, rhetoric, and logic, the trivium; arithmetic, geometry astronomy, and music, the quadrivium. Medieval encyclopedias reflected this arrangement. Since the universities were arranged according to the same system, and students studied according to it also, the arrangement was useful in education.
[How to Read a Book (1972), P. 180] "
― Mortimer J. Adler and Charles Van Doren