Final answer:
In Borges's short story, he explores the idea of identity by acknowledging the existence of two separate parts of his own identity: himself and the protagonist.
Step-by-step explanation:
In Borges's short story, he develops the idea of identity by acknowledging that there are two separate parts of his own identity: himself and the protagonist. This can be seen through his use of fragmented narration and reflective dialogue across time. The protagonist's realization of these dual identities contributes to the exploration of the theme of identity in the story.