Paragraph

The oldest classical British and Latin writings had little or no space between words and could be written in boustrophedon (alternating directions).

[1] The Greek parágraphos evolved into the pilcrow (¶), which in English manuscripts in the Middle Ages can be seen inserted inline between sentences.

A second common modern English style is to use no indenting, but add vertical white space to create "block paragraphs."

On a typewriter, a double carriage return produces a blank line for this purpose; professional typesetters (or word processing software) may put in an arbitrary vertical space by adjusting leading.

[2]The Elements of Typographic Style states that "at least one en [space]" should be used to indent paragraphs after the first,[2] noting that that is the "practical minimum".

[3] Miles Tinker, in his book Legibility of Print, concluded that indenting the first line of paragraphs increases readability by 7%, on average.

The software may apply vertical white space or indenting at paragraph breaks, depending on the selected style.

An alternative is to only put newlines at the end of each paragraph, and leave word wrapping up to the application that displays or processes the text.

This extra space, especially when co-occurring at a page or section break, may contain a special symbol known as a dinkus, a fleuron, or a stylistic dingbat.

For example, newspapers, scientific journals, and fictional essays have somewhat different conventions for the placement of paragraph breaks.

Topic sentences are largely a phenomenon of school-based writing, and the convention does not necessarily obtain in other contexts.