When a writer uses different speech patterns to distinguish characters in story make his fiction narrative more convincing what literary device is he using?

The literary device you're describing is called dialect.

Here's why:

* Dialect refers to the specific way a group of people speak, including their pronunciation, grammar, and vocabulary.

* By using distinct dialects for different characters, a writer can create more realistic and believable portrayals of those characters.

* It helps to establish their background, personality, and social standing, adding depth and authenticity to the story.

Example:

* A character from a rural area might use slang and colloquialisms that a character from a city wouldn't.

* An educated character might speak with more formal grammar and vocabulary compared to a less educated character.

This use of dialect is a powerful tool for writers to bring their characters to life and enhance the overall impact of their story.