I'm recycling a previous blog because recent editing of a novel brought up something new
about the subject. Here is the sentence in question:
Her blue eyes flickered in friendship, then retreated into inscrutability.
Apparently, some publishers' editing guides omit the comma:
Her blue eyes flickered in friendship then retreated into inscrutability.
The grammatical problem with omitting the comma is that dictionaries list the word "then" as an adverb or adjective but not, as that last sentence uses it, as a conjunction. Grammar requires either the conjunction "and" (or a comma plus "and") before "then"—or else just the comma to mark the omission of "and."
Researching that problem further on the internet, I found only one instance of the omitted comma. The site http://english.stackexchange.com/questions/4828/comma-in-compound-complex-sentences lists this sentence as correct:
I picked up my paycheck then paid my bills.
However, that site concedes that "most people would instinctively add 'and' before 'then' to allow for the comma between two independent clauses."
I picked up my paycheck, and then paid my bills.
That site also invites critiques by readers, so I submitted a comment that the sentence without comma or "and" was ungrammatical because it uses an adverb/adjective as a conjunction.
These abstruse questions of grammar will not affect the next presidential election or the price of oil on the international market, but they do affect our reputations as writers. And correct usage in this case allows writers to use punctuation of compound predicates to help dramatize the actions they describe.
Toward this end, the literary critic Stanley Fish wrote several decades ago that a sentence means everything that happens to the reader as he progresses through it. In our instance today, the writer can apply this principle to compound predicates. Here is a sentence that can be written and punctuated two ways:
The man hesitated and then spoke.
The man hesitated, then spoke.
The comma forces a pause, dramatizing the man’s hesitation. But that dramatization is lost if the sentence is written with the “and,” rushing the reader through to the second action. Here is another example:
The rifle held steady, then wavered.
The rifle held steady and then wavered.
The first example dramatizes the action of holding steady and the pause before wavering; the second deemphasizes the steadiness and rushes the reader through to the action of wavering.
The principle is this: Use the “and” to rush the reader through the sentence to suggest continuous action, but substitute the comma for “and” to make the reader pause, suggesting a time lapse or at least separation of the predicate’s two actions. Here are several examples from my novel Deadly Additive, written both ways here for comparison of effect:
Kristin and Jocelyn exchanged a questioning glance, then stared again at the door.
Kristin and Jocelyn exchanged a questioning glance and then stared again at the door.
She shivered once, then steeled herself to endure a long, cold night.
She shivered once and then steeled herself to endure a long, cold night.
After jogging half a mile he paused to catch his breath and then proceeded at a walk.
He took a sip of his drink, then started in alarm.
He took a sip of his drink and then started in alarm.
Both forms are acceptable, but the effect is different—a matter for the writer to choose the one more appropriate for the narrative situation.
Speed readers will not notice the difference, of course, but then speed readers miss much that the text of a novel contains.