Editors developed the subject index as a general guide to a variety of historical topics within Lincoln's legal practice. Most of the terms are general in nature and require little technical definition. The editors who assigned subject entries interpreted most entries very broadly. For example, they assigned the subject entry of "Animals--Horses" to cases in which the parties quarreled over the ownership of a horse, but also to cases in which someone stole a horse, the court seized a horse for a debt, or someone slanderously accused another of stealing a horse.
There are a few important exceptions to this policy of assigning subject entries broadly. The subjects "Bonds and Covenants, Litigation Involving," "Corporations," "Deeds, Litigation Involving," "Evidence," "Principal and Surety," and "Satisfaction of Judgment" were applied only to those cases in which such documents or activities were the issue of the case. Including all cases that had a bond of any sort, for instance, would have yielded results so numerous as to make the subject entry useless.
The subject entry "Pleading and Practice" was likewise applied only to those cases and activities in which issues of the forms of pleading and practice came into dispute. In its broadest sense, "Pleading and Practice" applies to all cases because they were governed by rules of pleading and practice, but using such a definition would have rendered the subject entry useless. Instead, the editors applied the entry in a more limited way only to those cases where issues of pleading and practice became important to the resolution of the case. Illinois Supreme Court cases, for example, were often appeals from lower courts in which technical issues of pleading or practice were at issue.
Some subject entries apply to only one or a handful of cases, which are known by a nickname or general name. Subject entries for the "Effie Afton Case" and the "McLean County Tax Case" direct users to the Hurd et al. v. Rock Island Bridge Co. and McLean County v. Illinois Central RR cases, respectively. A search for the second entry also yields Lincoln v. Illinois Central RR, in which Lincoln sued the railroad to collect his attorney's fees from the first case.