Are rules the same as principles? No, they ain't completely the same!
Principle is rule used to choose among solutions to a problem. Principle allows for diversified view of a matter or a problem, being guided by principle(s) is not as rigid as being governed by rule(s).
Where is there is principle:
based on individual's trained intellect, decision is made, but it isn't the same with individuals (untrained intellect) who ain't sure of how to go about a matter or problem let alone preferring solution, rules has to be in place as a good guide.