principal: most important, consequential, or influential
principle: a comprehensive and fundamental law, doctrine, or assumption
—Merriam–Webster

I still remember one of my elementary school teachers teaching me this tip to remember the correct endings of these two words. She’d say, “The principal is your pal.” While this may have painted an overly rosy view of people who hold the “most important, consequential, or influential” positions within schools (I’m looking at you, Mr. Saxton), it worked.

Example: Mr. Saxton was a really mean principal. He was so not my pal.

However, principal doesn’t have to refer to a person who has that as a title. It can refer to just about anything that has been given the most important, consequential, or influential role.

Example: Chocolate is the principal ingredient in the dessert.
Example: The principal thought to take away from the lesson is: cat videos are funny.

Note that in the first example sentence, principal is a noun. Meanwhile, in the last two sentences, principal is an adjective. Principal can be both a noun and an adjective. However, principle can only be a noun.

Here are some examples of principle:

Example: Ralph had a set of strict principles he used to guide his actions.
Example: It took Steve years to learn the top two principles of being a good step-father: grow a mustache and buy lots of presents.

Quiz:
Test your knowledge with this quiz. Fill in either principal or principle in the blanks. The answers are below.

1. The _______ reason Paula broke up with Paul is because his armpits smelled.
2. After reading the handbook, Lawrence knew the _______ that governed his workplace.
3. Martha misbehaved in class, so she had to meet with the school’s _______.
4. Liz found the religion’s _______ to be flawed, so she stopped going to church.
5. The _______ weapon in their arsenal failed, and the enemy was able to enter their territory.

Answers:

1. principal 2. principle 3. principal 4. principle 5. principal