Occasionally I’m asked the question “Why are these names not mentioned in the index?”
As a rule, all names should be in the index, except when they are passing mentions. The clearest case is when the name is used for illustration.
Here’s an example from the Remarkable Retail by Steven Dennis:
…[T]he stated goal of being the Casper of adult incontinence, the Bonobos of work boots, the Uber for tenured professors,....
On reading this, even if you don’t know what Casper is, you get the point from the context that is about the desire to be a disruptive retailer. And if you looked up Casper in the index and it brought you here, you would be annoyed because there is nothing here that’s actually about Casper. That’s why Casper is not in the index.
This example is from Humankind by Brad Aronson:
Saying yes to others can make all the difference. Besides helping people like Julius and Caloua get a start in life, it can change the world for a homeless teen…
Julius and Caloua are in the index, but there is no entry pointing to this paragraph. Their homeless situation is discussed elsewhere in the book, but there is nothing here about them specifically. Sending the reader here would be like sending them on a wild goose chase.
Now here’s an example where some indexers would omit the name, but I decided to include it. From Humankind:
Since getting his goldendoodle, Mulder, Joe’s life has changed radically.
Mulder is Joe’s service dog. In the index for this book I captured the names of all service dogs, many of which were described in detail. For consistency, Mulder was included, even though the dog is mentioned just this once. Mulder may be a minor character, but there is still something to learn about Mulder.
Besides, I thought, wouldn’t it be wonderful for Joe and his family if they picked up this book and saw that Mulder has a place the index!
So the rule of thumb is that names that are passing mentions are not indexed. This helps keep the index efficient for the reader. But identifying what is a passing mention is always an exercise in judgement.