André-Charles Caillot Issues a Bibliographical Guide to Antiquarian Bookselling and Collecting, with a Pioneering Exposition on Rarity

In 1790 antiquarian bookseller and publisher André-Charles Caillot published in 3 volumes Dictionnaire bibliographique, historique et critique des livres rares,

précieux, singulier, curieux, estimés et recherchés qui n'ont aucun prix fix, tant des auteurs connus que de ceux qui ne le sont pas, soit manuscrits, avant & depuis l'invention de l'Imprimerie; soit imprimés, et qui ont paru successivement de nos jours, en François, Grec, Latin, Italien, Espagnol, Anglis, & c. Avec leur valeur. Réduite à une just appréciation, suivant les prix auxquels ils ont été portés dans les ventes publiques, depuis la fin du XVIIe. Siecle jusqu'à présent. Auxquels on a ajouté, des observations & des Notes pour faciliter la connoissance exact & certaine des Editions originales, & les Remarques pour les distinguer les Editions contrefaits. Suivi d'n Essai de Bibliographie, où il est traité de la Connoissance & de l'Amour des Livres, de leurs divers degrés de rareté, & c. &c. Ouvrage utile et nécessaire A tous Littérateurs, Bibliographes, Bibliophiles, & à tous ceux qui veulent exercer, avec quelques connoissances, la Librairie ancienne et moderne.

In the introduction to their work the authors, who are not identified, explain how they were influenced by the Bibliographie instructive; ou traité de la connoissance des livres rares et singuliers issued by antiquarian bookseller Guillaume de Bure in 9 volumes from 1763 to 1769. They also provided a 10-page listing of the catalogues of about 100 auction sales of rare books that took place mainly in Paris from 1708 onward, together with the printed catalogues of a few private libraries, including the Catalogus Bibliothecae Thuanae (1679), from which they compiled their work. 

Perhaps the most notable feature of the work was the Essai de bibliographie, ou De la connissance & de l'amour des Livres, de leurs divers degrés de rareté, de la maniere de les classer, & de l'ordre de leurs facultés published on pp. 484-524 of volume 3.  This is one of the earliest discussions of the qualities of rarity in books, discussing the difference between absolute and relative rarity. By absolute rarity the authors meant books which were published in very small numbers, suppressed, or censored. By relative rarity they meant books which are sought after, collected or in demand even though they may be more or less common. In a footnote on p. 492 the authors referred to increased numbers of printers, lost morality, and increased production of scandalous, libellous or obscene literature as a result of the French Revolution.  In the Essai de bibliographie the authors also presented their refinement and expansion of the five basic subject categories under which information was organized in France since the beginning of the eighteenth century. 

In 1802 antiquarian bookseller and bibliographer Jacques Charles Brunet published a fourth and supplementary volume to this work. In the preface to that volume Brunet stated that the authors of the work, which was published by Caillot without attribution of authorship, were the abbé R. Duclos and the bookseller-publisher André-Charles Caillot.