rudiments vs first principles

rudiments and first principles both are nouns.

Word	Noun	Adjective	Verb	Adverb
rudiments	Yes	No	No	No
first principles	Yes	No	No	No

As nouns, rudiments and first principles are synonyms defined as:

rudiments and first principles: the elementary stages of any subject (usually plural)

Other synonyms of rudiments include alphabet.

rudiments (noun)	first principles (noun)
the elementary stages of any subject (usually plural)	the elementary stages of any subject (usually plural)
a statement of fundamental facts or principles