Normally, primary source is used to refer to a piece of text which offers the first thought on a specific subject. A secondary source, therefore, is a text which refers to the primary source. In example, the Declaration of Independence would be a primary source and anything written regarding the Declaration of Independence would be a secondary source.

That being said, one could (loosely) consider Hemingway's novel The Sun Also Rises a primary source based upon the fact that it is his own original work. But, one does not typically refer to a fictional novel as a primary source.

To expand on the idea, a published critical analysis on the novel would be considered a secondary source given it refers to, and quotes, the primary source.

How is The Sun Also Rises a secondary source?

The Sun Also Rises is a primary source if you are writing as essay on this novel.

Primary sources are inside works, in a manner of speaking. When writing about a work of literature, or a work of art of any kind, the art will be the primary source. Secondary sources are outside works that comment on the primary source or supplement it.

For instance, if you are writing an essay on The Sun Also Rises and you look at a quote from Gertrude Stein or a passage from a work of literary criticism these will be secondary sources.

However, if you are writing an essay on bull fighting instead of The Sun Also Rises, the novel can then be understood as something other than a primary source.