Aprenda a Diferença
comentada em 16/02/2020 18:26

For the curious ones out there:

A school principal is in the US; in UK and commonwealth areas the headteacher is responsible for the running of a school, managing staff and ensuring all pupils receive the most out of their education. They may work in a primary or secondary school, or even as Head of a college. Headteacher being the usual word in job applications and daily talk.

VERB + PRINCIPLE: establish, lay down, apply
PRINCIPLE + VERB:
apply, underlie, compromise as in the example sentences - This principle applies to all kinds of selling. This principle underlies Western philosophy, I refuse to compromise my principles by eating canned food. Also: adhere to, stick to as in - She sticks to the principle that everyone should be treated equally.

The prepositions IN or ON make a difference in meaning:
We agree with you in principle, but we'll need to discuss the details.
He refused on principle to agree to the terms of the treaty. He doesn't invest in the arms industry on principle. He would vote against it on principle.

Common phrases: a matter of principle They reject the proposal as a matter of principle. A person of principle.

Principal also can be someone or something that give or control the rules. I worked in some projects in that the customer referred himself as principal. For example: to make any deviation in its technical specification was necessary solicit the Principal approval

Indeed. The customer rightly said so; in law/business Principal is the part in an action or transaction having control or authority. Or as the popular  saying goes “the customer is always right”  :)