Confession: I have no idea where to put a paragraph break.
It started earlier in the year when I read Nicole Dennis-Benn’s Here Comes The Sun and Lara Vapynar’s Still Here back-to-back. Both novels have paragraphs containing dialogue spoken by more than one character. Since then, I’ve seen it in other books, including Claire Vaye Watkins’s Gold Fame Citrus; and, most confusingly, in a non-fiction book I read for research where the author divided a list between two paragraphs for no ascertainable reason.
Compounded with a recent workshop experience where I read aloud the opening to a short story: when I arrived at the last sentence of the paragraph, I read into the next paragraph because it didn’t feel like the natural ending point. Seven sentences in total, four in the first paragraph and three in the second (that went on for another nine), and I managed to confuse my workshop participants to the point that we all thought I had a different manuscript draft.
Strunk & White said, “Make the paragraph the unit of composition…As long as it holds together, a paragraph may be of any length – a single, short sentence or a passage of great duration.” 
One of my graduate school advisors said paragraphs are built of sentences made up of words with impact, meaning, and intention.
In How To Write, Gertrude Stein wrote with interesting punctuation, “The sentence is not emotional a paragraph is.”
I don’t need a prescriptive recipe to write one –– i.e., four sentences, the first of which is a thesis statement, the last of which concludes the paragraph –– but as I see examples like Dennis-Benn, Vapynar and Watkins, and take the aforementioned advice, the paragraph is becoming more elusive, less concrete.
Maybe that’s what Stein meant when she said it should be emotional. Or what my advisor meant. With all things in writing, it just has to work for that collection of sentences and ideas, that page, that story. Rules don’t matter. Ideas do. As long as those are clearly expressed, they can take any form.
 Strunk, Jr. William. The Elements of Style. Fourth ed. Allyn & Bacon, 2000.
Melissa Koss is a Senior Associate Fiction Editor for The Flexible Persona.