Another innovation frequently credited to Johnson is that of introducing illustrative quotations into monolingual English dictionaries. It had been the practice to include citations in Latin and Greek lexicons, but Johnson has been thought to be the first lexicographer to introduce quotations from modern authors (that is, from the Renaissance onwards) into an English dictionary, and, in fact, the point has been made that by doing so, Johnson was making these authors into modern classics. But it had been the practice in law dictionaries to cite authorities in nearly every entry, as though offering a textual precedent for the interpretation of the word, and most law dictionaries, going right back to Cowell, have citations in them.

The issue of definition is of the utmost importance in the law because the interpretation of the meanings of words in texts - writs, statutes, wills, and testaments - constitutes a large part of the business of the law. These words function as specialist terms and those who are professionally engaged in the law need to agree on their meaning. Crucially, then, their meaning depends on usage, on arbitrary custom and practice, rather than on purist notions of etymology. For this reason the usage of professional lawyers is cited to determine meaning, much as precedents are cited in the common law.

Johnson clearly thinks of language as operating on analogy with the law when he writes his Plan in 1747. Here he presents the usage of various writers as if they were testimonies of witnesses in a court of law, each of them offering a precedent which might influence the course of the common language in the same way as legal precedents affect the constitution of the common law:

I shall therefore, since the rules of stile, like those of law, arise from precedents often repeated, collect the testimonies of both sides, and endeavour to discover and promulgate the decrees of custom, who has so long possessed whether by right or by usurpation, the sovereignty of words.