The rule I want to introduce involves when to capitalize ranks in the military. There are three instances when rank is used: to replace a name, article/adjective/pronoun+rank to replace a name, and as a title before someone's name. Examples:
To replace a name: Let's say Tom is a lieutenant. "Come here, Tom" would more likely be written as "Come here, Lieutenant." Similar to how Mother and Father are capitalized when they replace the parents' names, if the title is used in place of the soldier's name, it is capitalized. This happens most often in dialogue.
art/adj/pro+rank replace a name: Tom is still a lieutenant. If the text reads "Tom gathered firewood as commanded," it could also read, "The lieutenant gathered firewood as commanded." Because the article the is present, lieutenant is not capitalized. It would make no sense to read, "The Tom gathered firewood." The presence of an article, adjective, pronoun--anything that introduces a noun--means that the rank is not capitalized regardless of the situation: a captain, those sergeants, angry generals.
As a title: This is probably the most intuitive. Although there are exceptions, if a title precedes someone's name, it is capitalized: Lieutenant Tom, General Stonewall, Commander-in-Chief Obama.
These rules aren't that complicated, but because ranks aren't always either capitalized or not, it's easy to mix up when I'm in the middle of editing. I'm already looking out for punctuation and spelling and sentence flow; it's hard to add in how a rank is being used in order to determine if it needs to be capitalized. Often I'll be twenty pages (or more) into a book and I'll realize that the author is always capitalizing ranks, and I'll have to go back and change it. Often I'll ctrl+f each rank mentioned in the manuscript and just make sure I've capitalized them correctly according to context.
The following excerpt is pulled from a manuscript I edited about two brothers--twins--who are fighting on opposite sides of the Civil War. Sel is fighting for the North and he is just meeting his commanding officer. This was the passage when I realized I hadn't been paying attention to rank capitalization.
“Did
they tell you anything about this assignment, Private Danner?” called the lieutenant
over the clatter of hooves on cobblestones. There had been no snow in Baltimore
as there had been in Frederick and Washington.
“No,
sir,” replied Sel.
“Well,
Private, you are qualified for this mission due to one important
accomplishment.”
“What’s
that, sir?”
“You
were born in Frederick.”
“It’s
good to know I’ve done something worthwhile,” said Sel. He could feel
Lieutenant Dorsey watch him as they rode toward the outskirts of the city.