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Common Mistakes and Confusing Words in English
Principal as an adjective means first in order of importance:
For example: The Mississippi is the principal river of the United States.
Principal as a noun can mean the head teacher in a school or college:
For example: The teacher sent the unruly student to see the principal.
Principal as a noun can also mean the original amount of a debt on which interest is calculated
For example: She lives off the interest and tries to keep the principal intact.
Principle is a noun which means a basic idea, standard of behaviour or rule that explains or controls how something happens or works:
For example: The country works on the principle that all citizens have equal rights.
!Note - If you can't remember which is which, try this little mnemonic "The principal is your pal."