A rhetorical analysis looks at the author's use of language, his rhetorical devices, style, and tone. Hemingway has a very distinct style: Walker Gibson calls his style "Tough" and "Plain," which is to say that he tells a story as simply and directly as possible without much adornment (adjectives, complex sentences). This style is, according to Professor Don Nilson:
1. the language of intimacy, the language of no pretensions. The words are simple and the grammar is simple.
2. the writing is not planned, but just happens, in a stream of consciousness kind of way—you are there.
3. the sentences are short and choppy. If there is conjunction it is coordination, not subordination.
4. it is the language of the loosened tie and the rolled up shirt sleeves, with no pretentious multi-syllable or low-frequency words.
A rhetorical analysis looks at diction, sentence complexity, use of dialogue, point of view, and purpose--as well as the effects of all these upon an audience. So, Hemingway, an old man himself, is trying to humbly tell a story of another old man, Santiago, using a third person omniscient point of view (we know the old man's thoughts) and a sparse, minimalistic narrative. Hemingway adopted this style from being a journalist; he had to meet word counts and deadlines. His style is also very masculine: concrete word choice (not the flowery prose of a Romantic, let's say).
Hemingway's sentences are very simple. Many are compound: he uses "and" a lot to string together short sentences. This is called polysyndeton, the repetition and pairing of conjunctions ("and") in close succession for rhetorical effect. Observe the title: "Old Man and the Sea" and the first paragraph:
But after forty days without a fish the boy’s parents had told him that the old man was now definitely and finallysalao, which is the worst form of unlucky and the boy had gone at their orders in another boat which caught three good fish the first week. It made the boy sad to see the old man come in each day with his skiff empty andhe always went down to help him carry either the coiled lines or the gaff and harpoon and the sail that was furled around the mast. The sail was patched with flour sacksand, furled; it looked like the flag of permanent defeat.
Hemingway's use of "and" gives the narrative a rythym like the sea: it flows. It's also a bit of stream of consciousness, like thoughts floating onto paper. Hemingway uses everyday words, much like a fisherman would use, to achieve ethos, or a sense of trustworthiness in character--both his (as author) and Santiago (his protagonist).