My professor says I'm oversimplifying—can someone help me understand which two factors really drive authorial purpose?

[Gort]

I wrote a paper arguing that author's purpose is just about what the author wants—to persuade, inform, or entertain. My professor wrote in the margins: 'You're oversimplifying. Purpose emerges from the intersection of two key factors.' She wants me to revise and explain which two factors really drive authorial purpose. From our class readings on rhetorical context, I'm starting to think it's about the author and the audience working together.
The author brings their own motivations, background, and biases, but those only matter in relation to who they're writing for. A text's purpose isn't just what the author wants—it's what the author wants in relation to a specific audience. Is that it? Has anyone else had to write about this? I want to get this revision right.

 

[JaneCops]

Most models identify author, audience, and context as the big three, but your professor specifically said two factors—so author and audience is a strong pair.

The author brings intention, bias, background. The audience brings expectations, knowledge level, values. Purpose happens in the space between them—what the author wants the audience to think/feel/do.

I'd frame it exactly like that in your revision.