Negatives in Japanese

ない (non-exist) is the basis of negatives in Japanese. As it is describing something (a state of non-action) it is an adjective. Using ない to end a sentence negates the preceding clause.¹

Example: There is not a pen.

ペンがない

Info

ペン (pen) is marked by が so it is the core subject of the sentence.

ない is the adjective in this adjectival sentence. It says something about the core subject. In this case, it is saying that it does not exist. There is not a pen.

Footnotes

1. Japanese from Scratch (7) ↩