An essential unit of thought in writing, the paragraph usually consists of a group of related sentences, though occasionally no more than one sentence. The first line of a paragraph is indented, about one inch when handwritten and five spaces when typewritten.
--From the Harbrace College Handbook, 10th Edition by John C. Hodges and Mary E. Whitten
This unreadable paragraph comes straight out of a textbook on writing. In the first sentence, the authors obscure one possibly useful fact with mislaid clauses and confused writing. The second sentence is mere trivia.
Sadly, students who read too many condescendingly written and content-free "essential units of thought" like this one will get worse at writing. Crap writing like this is particularly contagious among those who confuse convoluted thinking with intelligence.
All across our country, we are giving our students reading assignments out of textbooks just like this one--textbooks that will surely maim, if not kill, a young person's desire to write.
If you are a textbook writer, please, please keep this in mind.