Rather than repeat information that can be found elsewhere on the blog, I have added hyperlinks to other writing concepts you should know.
Nonfiction writing requires three types of sentences: thesis, topic, and supporting.
(Seattle, if you are curious.)
An essay’s thesis statement resides in the introduction, and other blog posts cover their construction and use (here, here, and here). Topic sentences define the parameters for paragraphs. Everything else is supporting detail.
Some writing is constructed with the “everything else” composed entirely of facts. Each point gets raised, defined, described, or analyzed as needed, and completed before the next point is introduced. Technical writers do this when they assemble instruction booklets and owners’ manuals. Students, too, sometimes build writing entirely from facts. Process essays, for example, move step by factual step through a documentation (lab reports, for example) or a how-to.
Most academic and non-fiction writing benefits from adding ethos. An expert could be, for example, the inventor of an object, an authority on a method, the instigator of an event, or simply a quotable person on one side of an issue. Researching an essay topic will likely turn up several choices for expert opinions. By incorporating either an authority or a reasonable spokesperson, writers show readers that the essay is more than merely one person’s opinions, which (we will assume) increases their trust in the subject portrayal and analysis.
Even writing dedicated to straightforward facts might still have room for pathos, which can add more information, more color, more zing, than simple facts alone. In a history exam, for example, providing “more” comes from choosing words like ransacked instead of searched, commandeered instead of controlled, and violated instead of ruined. Every sentence won’t need “more,” so use pathos where the emphasis is needed — and be sure that extra bit of emotional shading remains truthful.
Pathos is not limited to only words and phrases; it can be entire paragraphs. Anecdotes in the introduction and/or conclusion make an essay more reader-friendly. Using a (true) human-interest story can be a smart way to ease readers into (and/or transition readers out of) an essay which contains complexities or covers a difficult subject. More importantly, well-chosen anecdotes can help an author establish the why this is important and to whom reasoning that lies behind the subject, and that is definitely supporting detail.
Recap: Supporting sentences in a paragraph expand on the idea in a paragraph’s topic sentence. They may include references to others’ opinions and/or their data. Also, as long as they continue to truthfully support the topic sentence, supporting sentences can include colorful language and short narratives.