Principle (meaning 'code' or 'law') is spelled differently than principal (meaning 'most important' or 'person or thing of great importance'). This serves to remind us that these are two different words, with different spellings and meanings.
Although they sound and appear alike, the terms principal and principle mean different things.
Principle is a noun, whereas principal can be either an adjective or a noun.
Principal is a noun that typically refers to the main or head individual, such as the principal of a school. (Some individuals recall this meaning by using the word “pal”)
As a noun, it can also refer to a large sum of money, someone who commits or aids and abets a crime, or someone who hires someone else (an agent) to represent them. Principal is an adjective that denotes "major" or "primary," such as the main discovery in a study.
A principle, on the other hand, is a term that denotes a law, precept, or fundamental truth, such as the law of gravitation.
Consequently, use principal as a noun to describe significant individuals and as an adjective used to denote a significant individual or object. In contrast, when referring to a law or doctrine, use the term principle.
Example:
The high school's principal led the pupils in singing the national song. (Principal is a noun that refers to the principal or chief individual.
If the defendant waived his right to a jury trial, that is the main question at stake in this case. (A principle is a noun denoting a main or primary)
The guiding ideals of our nation are freedom and justice. (Principle = rule, tenet, or fundamental fact)