At the watercooler the other day, one of my down-the-hall colleagues cranked up a discussion about persuasive writing. He had just come back from the office of an old-time appellate lawyer and prattled on about how this guy's brief didn't have a sentence in it longer than five words. "Crickey, even my ten-year old could read that!" While brevity and clarity usually go hand-in-hand, sometimes it's good to vary the length of your sentences to influence the reader's speed. For example, Gary Provost in his book, 100 Ways to Improve Your Writing, demonstrates the truth how the five-word-sentence rule might be one to avoid.
This sentence has five words. Here are five more words. Five-word sentences are fine. But several together become monotonous. Listen to what is happening. The writing is getting boring. The sound of it drones. It's like a stuck record. The ear demands some variety. Now listen. I vary the sentence length, and I create music. Music. The writing sings. It has a pleasant rhythm, a lilt, a harmony. I use short sentences. And I use sentences of medium length. And sometimes, when I am certain the reader is rested, I will engage him with a sentence of considerable length, a sentence that burns with energy and builds with all the impetus of a crescendo, the roll of the drums, the crash of the cymbals--sounds that say listen to this, it is important.