There is a rhythm to fluent language. There is an evenness. But, while excellent sentence fluency may be your goal, don’t disregard the power of interruption. Of silence.

Sentence Fluency is the rhythm and flow of the language, the sound of word patterns, the way in which the writing plays to the ear—not just to the eye. How does it sound when read aloud? That’s the test. Fluent writing has cadence, power, rhythm, and movement. It is free of awkward word patterns that slow the reader’s progress. Sentences vary in length and style, and are so well crafted that reading aloud is a pleasure.
—Source: random piece of paper @ 2004 from a graduate course that I recently retrieved from the floor of my home-office

Just like everything else related to writing and to art, there is a great deal of subjectivity involved. Where I find “sentence fluency,” you may not. But here are some examples that I particularly like:

At times I believed that the last page of my book and the last page of my life were one and the same, that when my book ended I’d end, a great wind would sweep through my rooms carrying the pages away, and when the air cleared of all those fluttering white sheets the room would be silent, the chair where I sat would be empty.”—The History of Love by Nicole Krauss

Once upon a time there was a boy. He lived in a village that no longer exists, in a house that no longer exists, on the edge of a field that no longer exists, where everything was discovered and everything was possible. A stick could be a sword. A pebble could be a diamond. A tree a castle.”—The History of Love by Nicole Krauss

Prince Andrey turned his scornful gaze on the endless, chaotic mass of detachments, wagons, supply vehicles, artillery and more wagons, wagons, wagons of every size and shape, overtaking one another and blocking the muddy road three and four abreast. On all sides, right up front and way behind, as far as the ear could strain in every direction, you could hear wheels rumbling, carts rattling, wagons creaking, gun-carriages groaning, horses trampling, whips cracking, drivers shouting and everybody swearing, soldiers, orderlies, and officers. The roadsides were littered everywhere with fallen horses, flayed and unflayed, broken-down wagons with solitary soldiers sitting by them just waiting, other soldiers separated from their units, heading in little groups for the next village or carrying loot from the last one—chickens, sheep, hay, or sackfuls of something or other. When the road went uphill or downhill, the crowds squashed together even closer, and there was an endless hubbub of shouts and groans. Soldiers floundering knee-deep in mud heaved guns and wagons along with their bare hands while the whips cracked, hoofs slithered, traces snapped and the air rang with the most heart-rending cries.—War and Peace by Leo Tolstoy translated into English by Anthony Briggs

You aren’t alive anywhere like you’re alive at fight club. When it’s you and one other guy under that one light in the middle of all those watching. Fight club isn’t about winning or losing fights. Fight club isn’t about words. You see a guy come to fight club for the first time, and his ass is a loaf of white bread. You see this guy here six months later, and he looks carved out of wood. This guy trusts himself to handle anything. There’s grunting and noise at fight club like at the gym, but fight club isn’t about looking good. There’s hysterical shouting in tongues like at church, and when you wake up Sunday afternoon you feel saved.”—Fight Club by Chuck Palaniuk

There’s something so wonderful and inspiring about writing. It casts a spell. You enter the realm of the mind where images appear and disappear, and language, so central to it all, seems to be irrelevant.

Assessing Sentence Fluency

• Sentence structure and length are varied. (Not robotic, not monotonous, not the same)
• Sentences have rhythm and grace. When you read them out loud, you don’t stumble.