The noun principle and the noun and adjective principal are often confused. Although pronounced alike, the words are not interchangeable in writing. A principle is broadly “a rule of action or conduct” (His overriding principle is greed) or “a fundamental doctrine or tenet” (Their principles do not permit the use of alcoholic beverages). The adjective principal has the general sense “chief, first, foremost”: My principal objection is the cost of the project. The noun principal has among other meanings “the head or director of a school” (The faculty supported the principal in her negotiations with the board) and “a capital sum, as distinguished from interest or profit” (The monthly payments go mostly for interest, leaving the principal practically untouched).
