If offered a choice, would you rather have principles or principals?

A principle is a fundamental or general truth. It might also be the original (fundamental) source of something.

America's principles establish religious liberty as a fundamental right.

In principle refers to something in its fundamentals without all the details worked out:

After just one hearing, Arroyo's bill penalizing drunk driving and five other similar bills were approved "in principle" by the committee on transportation.

Principal, on the other hand, is the person with the highest authority in a group, such as a school principal or the principal investor in a company. It is also the original sum of money or assets invested or lent:

An Israeli high school principal has been summoned for a hearing by the country's Education Ministry.

Jan van Eck serves as a director and principal at the firm.

The FHA refinance plan for homeowners may allow for principal reductions and underwater refinancing opportunities for those who qualify.

If you remember that the principal is your pal, you'll be able to choose your words well.