Principal / Principle
Different meaningsPrincipal can mean chief or most important; principle is a rule or fundamental belief.
Principal
Use when
You mean the most important, or a person or sum in a leading role.
Example
“The principal reason for the change is service reliability.”
Principle
Use when
You mean a fundamental rule, belief or standard.
Example
“Accessibility is a core design principle.”
Quick check
guiding principal, principle reason
Usage note