I was solving a grammar exercise from the book, Word Power Made Easy, when I came across this question
A feeling of one's worth is one of the principle/principal goals of psychological therapy.
Going by the same rule which has been taught in every school that:
Principle : Rule, standard
Principal : Head( Usually a person)
I marked principle which is wrong, the correct answer according to the book is Principal.
Pondering over the question for a few minutes, I came to this conclusion that principal is not always a person and can refer to the "head or main" point, as in referring to the sentence "the main goals of psychological therapy"
I also looked at this question here "Principal” or “principle”, but it didn't help me either as it says principal usually refers to a person.
My question is, is it necessary to use principal as a person or it can mean something else as well?