All 3 Uses of

principle
in
Of Human Bondage

In his clerical dress there was indeed something in him to suggest the tar-barrel; and though on principle he gave five hundred lines to any boy on whose lips he overheard his nickname, at dinner-parties in the precincts he often made little jokes about it.†
Chpt 17-18

on principle = because of a basic rule or belief

To Mr. Goodworthy, a respectable householder with excellent principles, the capital of France was a paradise of the joyously obscene.†
Chpt 37-38 *

principles = basic rules or beliefs

Oh, my principle is to profit by all the benefits that society provides.†
Chpt 85-86

principle = basic rule or belief

Definitions:

(1) (principle)
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
(2) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

See a comprehensive dictionary for more specialized senses including one in chemistry.