Author’s purpose

Every passage is written to do something. The four most common purposes are:

• Inform — present facts neutrally.
• Persuade — convince the reader to accept a position.
• Narrate — tell a story.
• Entertain — amuse the reader.

How to tell

• Look at the tone: neutral and factual? Charged and argumentative? Personal and reflective?
• Look at the structure: lists and definitions? Claim + evidence + counter-claim? Scenes with characters?
• Look at the diction: technical terms? Loaded vocabulary? Sensory description?

Example

"Coffee is the best drink in the world. No serious morning starts without it."

This is persuade: opinion, charged adjective ("best"), and a generalization with no evidence.