On grammatical class:

ja'aku
(adverbial) bridi logical affirmer; "it is true that...."; affirms the bridi as well as any other adverbial or quantifier located on its right.
naku
(adverbial) bridi contradictory negator; "it is not true that...."; negates the bridi as well as any other adverbial or quantifier located on its right.

In notes:

na'ei
Contradictory negation of a predicate
adverbi
x1 is an adverbial adjunct (adverb or adverbial clause) meaning x2 in language x3