We are accustomed as teachers to insist that our students (those doing exams, anyway) paragraph properly. It is, we tell them, the natural unit of thought. Paragraphs have repeatable structure: topic and exemplification, for instance,
where the exemplification is a form of embedded list; or topic and detailed elucidation. And so on.
But the paragraph is perhaps not such a clearly rooted structure as it seems to us, certainly for inheritors of intellectual traditions other than the Greek. The paragraph was originally not a discrete block of text marked out from other blocks of text; text in manuscript were through composed, with various marks or signs introduced here and there to indicated breaks of thought or new ideas – a process known as rubrication, from the red-letter manuscript insertions.
One slightly later form of rubrication was the introduction of the pilcrow – ¶ – a sign still in use today among proof-readers (and word-processors, if you switch on your mark-up).
Some time after the introduction of print, the paragraph became detached as a period of thought, roughly contemporaneously with the appearance of other purely textual phenomena such as the title page, the index, and the list. Texts started to take on the characteristic of a thing rather than an utterance, with physical spatial relations, a sort of visualisation of the forces of thought.
But not all thought runs in these, for us, deeply grooved channels. The somewhat legalistic (actually, rhetorical) forms of thought, where arguments are presented and then defended or supported, is derived from Greek practice and its subsequently codification by the Romans. Other intellectual traditions, (Indian, Chinese) tended to avoid, smooth, or reconcile conflict in ideas.
So when we ask our Chinese or Japanese students, for example, to paragraph an IELTS part 2 essay, we are asking a lot more than we sometimes realise.