All 3 Uses of

principle

in

Don Quixote

fear led him to the same spot to which Don Quixote and Sancho Panza had been led by theirs, just in time to recognise them and leave them to fall asleep: and as the wicked are always ungrateful, and necessity leads to evildoing, and immediate advantage overcomes all considerations of the future, Gines, who was neither grateful nor well-principled, made up his mind to steal Sancho Panza's ass, not troubling himself about Rocinante, as being a prize that was no good either to pledge or sell.†
Chpt 1.23-24

principled = with or based on basic beliefs

laws of art will only find some half-dozen intelligent people to understand them, while all the rest remain blind to the merit of their composition; and that for themselves it is better to get bread from the many than praise from the few; then my book will fare the same way, after I have burnt off my eyebrows in trying to observe the principles I have spoken of, and I shall be 'the tailor of the corner.'†
Chpt 1.47-48 *

principles = basic rules or beliefs

' "'Those are the ones I mean,' said I; 'and see if they did not observe the principles of art, and if, by observing them, they failed to show their superiority and please all the world; so that the fault does not lie with the public that insists upon nonsense, but with those who don't know how to produce something else.†
Chpt 1.47-48

Definition:

a basic rule or belief

The exact meaning of principle can depend upon its context. For example:

"our guiding principles" -- basic moral beliefs that guide decisions and behavior
"electromagnetic principles" -- rules describing how the world works
"She lacks principles." -- lacks moral guidelines
"We agree in principle." -- about important basic beliefs