Some time ago a client asked me how I decide when to use cross-references and why certain arrays have cross-references and not others. Which is a good question. I decided to sit down and outline all of the different scenarios in which I use—or don’t use—cross-references, and, well, the list is a lot longer than I expected. So, I’m going to split this reflection in half. Part two to come in a couple of weeks.

As a very brief introduction, cross-references are like signposts that redirect readers to a different array in the index. Cross-references can either be See references (“aubergine. See eggplant”) or See also references (“Brassica, 34, 56-57, 63. See also cabbage”).

From General to Specific

Perhaps the most common scenario is to direct readers from general information to specific information. This is especially true if the more specific array has subheadings. Instead of double-posting or sub-subheadings, redirecting readers can be more space efficient and easier to read.

One way to think about the levels of information in a book and index is as a cascade. Information flows down, from most broad to most specific. Cross-references usually move in that direction too. To give an example, a book I recently indexed is about the key chemical elements nitrogen, phosphorus, and potassium. There is a brief discussion about chemical elements as a whole, and so I’ve included cross-references from the general (elements, chemical) to the specific (nitrogen, phosphorus, and potassium). 

From Specific to General

Can cross-references go in the opposite direction? I don’t want to say never, because it can happen, but I think it is less common. My assumption is that broader terms may be easier to remember, and if readers want to find the broader term, they would have started there anyway. So while I often create cross-references from the general to specific, following the cascade of information, I usually don’t make those cross-references reciprocal.

One exception is if the general term is the preferred term. Going back to the book on nitrogen, phosphorus, and potassium, fertilizer is a significant subject. For the most part, the discussion is about mineral fertilizers (also known as synthetic fertilizers). But while the terms mineral and synthetic fertilizers are defined, they are not actually used a whole lot in the text. Rather, it is implied that “fertilizer” usually means mineral fertilizer. Similarly, I suspect most readers will first search for “fertilizer.” So while I do include main entries for mineral and synthetic fertilizers (mostly for their definitions), I primarily use those entries to cross-reference to fertilizer.

Reciprocal Cross-references

As I mentioned, I don’t often include reciprocal cross-references from specific to general terms. But reciprocal cross-references are important in their own right. I usually use them for related headings that have equal weight. 

By equal weight, I mean that they are at about the same level of granularity or importance. This can include synonyms. Both arrays contain subheadings and/or locators, and readers searching for one may reasonably be interested in the other.

For example, a reader searching for the term “liberty” may also be interested in “freedom.” Facebook, the social media platform, should probably be linked to its parent company, Meta, and vice versa. Terms which belong to the same category can also be linked together with reciprocal cross-references. For example, an index with arrays for electrons, neutrons, and protons could include cross-references between all three terms. 

Preferred Terms

Reciprocal cross-references work best when both arrays contain searchable information. If only one array contains locators, or if there is otherwise a clear preference for one term over others, then a See cross-reference is needed to direct readers to the preferred term.

Preferred terms can come about for a number of reasons. There may be enough locators to warrant subheadings, and so a preferred term is chosen to gather the discussion in one place. The author and text may also emphasize one term over another. Perhaps a certain term is more inclusive or better reflects current usage. Whatever the reason, a See cross-reference anticipates that readers might look elsewhere and points readers in the right direction. 

Cross-References versus Double-Posts

Synonymous terms can raise the question of whether it is better to double-post. If “feelings” and “emotions” are both used in the text, are used in the same way, and used about the same number of times each—they carry about equal weight—then why not double-post under both instead of using cross-references? 

Double-posts and cross-references are like indexing twins. They both serve to provide alternative entry points, and there are situations in which double-posts can be the better option. Instead of sending readers off in a new direction, readers can find the relevant locators right where they are. In the above example, there are times when I have double-posted something like “feelings and emotions” and “emotions and feelings.”

My general rule of thumb is to double-post if there are no subheadings and to use a cross-reference if there are subheadings. Subheadings take up more space, and so it is more space efficient to redirect.

The other reason to choose cross-references is if there is a preferred term. Synonymous and related terms do not always have equal weight. If the text clearly prefers a term, or if a term is clearly preferable for another reason, then that should be reflected in the index

 

I’ll stop here for now. I’ll write again in a couple of weeks to discuss general cross-references, cross-references from subheadings, and cross-references to and from acronyms.

For now, keep in mind that cross-references are a versatile and powerful tool for shaping how readers navigate the index. If you can map out the structure of the index, with all information in its place, cross-references are the signposts that points readers to where they need to be.