Edit 4/15/14: "The topic sentence (the first sentence of each paragraph) is the most powerful weapon in every writer's arsenal." - editor Lizzie Towl, via The Thesis Whisperer
Quick, what's a paragraph? Is it a group of 3-5 sentences on a similar topic? Is it a topic sentence followed by a few illustrative sentences? These two common grade-school definitions of the paragraph are certainly useful, even to the writer who has graduated from writing five-paragraph essays to writing high-level academic prose. Still, though, these definitions do not capture everything that a paragraph must do for the thesis or dissertation writer. In a long, complex academic argument, the paragraph has a crucial organizational function: the author uses paragraphs to signal to the reader what the various components of the argument are and how those components fit together. The point about paragraphs that I find myself most emphasizing with clients is that paragraphs are building blocks.
So, what does it mean for every paragraph in your thesis or dissertation to be a building block, a unit of organization, in your argument as a whole?
* Each paragraph begins with a topic sentence ("sub-claim") that is, through some logical chain, a "reason why" the reader should accept your main claim as true
* Each paragraph focuses on a single idea, one that's neither too large nor too small to fill out one-half to three-fourths of a page
* Each sentence flows logically from the one before it and to the one after it
* Each sentence and paragraph contains only relevant information
Such a strict view of paragraphing requires disciplined and careful writing, but the practice of paragraphing well is essential for any academic writer. Ultimately, your argument can only be as strong as the paragraphs that comprise it.