A definite article indicates that its noun is a particular one (or ones) being identified. It may be something that the speaker has already mentioned, or it may be something uniquely specified. The definite article in English, for both singular and plural nouns, is "the".
You should look up the definition of "principle". You are failing both the grammar and vocabulary sections at this point. A principle of something is not "equal to" that thing, whether it is singular or plural.
*sigh* I'm trying to discuss the subject matter and now I get, Let's argue word definitions. Is that really the best argument you want to make about the thread subject?