One point per paragraph
Aliases: topic sentence · one idea per paragraph · scannable paragraphs
What it is
A paragraph is a skimming unit. Two decisions or two conditions in one block, and the skimmer leaves with the first sentence. The exception in the second sentence was never written, as far as they are concerned. One idea per paragraph: the one thing this block should leave behind sits where a topic sentence would sit. Everything else starts a new block or becomes a list.
Why it happens
Web reading is often an F-shaped scan. The first sentence is taken as the proposition; the rest as detail. People under high load, or whose attention is easily pulled, may act after the first sentence. Tucking a refund exception, a deadline, a legal consequence into the back of the same paragraph is hiding it in “not yet scanned.”
Prose on paper can finish a claim-and-evidence move inside one paragraph. Public-service pages, settings copy, error recovery are not read to the end for their own sake. A list is more honest when the items are peer conditions: each line is a point, and none pretends to sit under a single topic sentence. Get the unit wrong and the sentences can be crystal; the second point still dies at the end of the block.
Studying it
Comprehension items must ask the second point at the end of the paragraph: the refund exception, the cutoff, the side effect. Compare two points in one paragraph against a split into two paragraphs or a list. Eye tracking or click maps show whether people enter the block that holds the exception.
Independent variables: ideas per paragraph, exception first versus last, paragraph versus list. Dependent variables: detection of the second point, actions taken on the wrong condition.
Whole-page reading time is a bad primary measure — the fast scanners are exactly the people who miss the tail.
Where it stops holding
Scholarship, literary prose, and genres that complete claim-and-evidence inside a paragraph already have two layers; splitting them on principle will shatter the argument. Tables already use the row as the point; wrapping “one paragraph” around them wrecks the structure. Chat bubbles are already short units; splitting again yields a string of one-sentence bubbles. A one-line warning banner cannot hold a paragraph structure — that is a different component.
Applying it
- On critical pages, label each paragraph with one sentence that is its point. Two labels means split, or make a list.
- Exceptions, deadlines and consequences get their own paragraph or their own line. Do not hang them off the main rule as a trailing clause.
- How to check: cover everything in each paragraph except the first sentence (or each list row) and ask “what does this block want you to do?” If the exception is invisible until sentence two, promote the exception to its own block.