Both Uses of

principle
in
The Importance of Being Earnest

There are principles at stake that one cannot surrender.†
Act 3

principles = basic rules or beliefs

The two weak points in our age are its want of principle and its want of profile.†
Act 3 *

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.