Doing Research at the Library of Congress

IIA. Three Basic Principles of Library of Congress Subject Headings

c. Specific entry

This concept is the most important of all; but it is in many ways counterintuitive. It means that catalogers will always try to assign the subject headings, from the LCSH list, that are the tightest fit for the book as a whole, and will not assign general headings when more appropriate narrower terms are available. Researchers often assume that general headings "include" the narrower subjects, too--but they do not. In practical terms, "specific entry" means that you should always start by searching with the most specific headings you can find--not with general headings, because the specific headings are not included in the general categories. This concept may perhaps be clarified by several examples of mistakes that even experienced researchers routinely make, such as the following:

• A student interested in nightmares made the mistake of looking under the general headings Sleep and Dreams. The proper heading is Nightmares. Works on nightmares are filed only under the latter term; they are not also filed under the more general headings.
• A researcher interested in the effects of divorce on children made the common mistake of looking under Divorce. The proper category is the narrower term Children of divorced parents; books under this heading are not duplicated under Divorce.
• A biologist looking for books on blue crabs wasted a lot of time combing through hundreds of entries under Crustaceans and Chesapeake Bay. The proper heading is Blue crabs, and books under this topic are not duplicated under the general headings.
• A reporter looking for material on television game shows made the mistake of searching under Television. The right heading is Game shows, and books under this term are not indexed under Television.
• An ethnologist looking for works on the Chibcha Indians of Colombia made the mistake of looking under the general heading Indians of South America. The proper term is Chibcha Indians, and works under this specific term are not duplicated under the more general heading.

In each case, the researchers mistakenly assumed that finding a general heading was the best way to start. This is one of the most common, and most serious, mistakes that you can make in using a library catalog. The rule is this: always start with the headings that are the tightest fit for what you have in mind, rather than with general headings, because the general headings do not include the narrower topics.

The general headings are there because some books are written at broad levels--thus, for example, some books are indeed written about divorce in general. Those works will receive the Divorce heading because that term is the tightest fit for works written at that broad level. But if you really want books on the effects of divorce on children, then you have to use Children of divorced parents because the LCSH list provides a tighter-fit category for that level.

There is a reason for this practice. If books about blue crabs were to be cataloged under general terms such as Crabs, Crustacea, or Chesapeake Bay then there would be no predictable or logical stopping point in either their assignment by catalogers or their selection by researchers; the same books could also just as logically be indexed under Arthropoda, Ecology, Estuaries, Invertebrates, Marine biology, Marine invertebrates, Coastal fauna, Oceanography, or any of two dozen other terms--all of which appear as valid headings in the red books. The problem is that when you search in the direction of generality there is no mechanism for choosing one heading rather than another, because all of them are potentially relevant. (If the system did not have a rule for choosing among such a variety of valid headings, it would not be "controlled" in the first place; its use would entail just as much guesswork as figuring out variant title keywords.) The solution is that when you search in the direction of specificity there is indeed a logical stopping point--Blue crabs--and it is predictably the best heading among all of the alternatives because of the rule of specific entry. In other words, LCSH is not just a list of terms; there is also a rule that goes with the list: look for the headings within it that are the tightest fit for your topic.