Doing Research at the Library of Congress
IIA. Three Basic Principles of Library of Congress Subject
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
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
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
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,
Bay then there would be no predictable or logical stopping point in
either their assignment by catalogers or their selection by researchers; the
books could also just as logically be indexed under Arthropoda, Ecology,
Estuaries, Invertebrates, Marine biology, Marine
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
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
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.
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