DE LUCA, GIOVANNI BATTISTA. Jurist, b. at Venosa in 1614, d. at Rome on 5 Feb. 1683. He studied jurisprudence at Salerno and Naples, where he obtained his degree at the age of 21 and practiced law for a long time until he moved to Rome in 1645. Having become an ecclesiastic, he served as auditor and secretary of memorials, and on 1 Sept. 1681 was created cardinal by Innocent XI.
His principal work is the *Theatrum veritatis et iustitiae, sive decisivi discursus per materias seu titulos distincti*, etc., in 21 volumes including supplements (Rome 1669–73 and Venice 1734): a kind of repertory containing, arranged by subject, the forensic arguments and discourses he delivered in the exercise of his profession. At the end of each book is appended a doctrinal exposition.
A reduction of this work into the Italian language was made by D. L. himself later, under the title *Il dottor volgare ovvero il compendio di tutta la legge civile, canonica, feudale e municipale nelle cose più ricevute nella pratica*, etc., in 15 books (Rome 1673). Also famous is his *Discorso dello stile legale*, in which he advocates, among other things, the use of the Italian language in judicial proceedings.
D. L. is the most representative figure of practical jurisprudence in the 17th century. He starts from a just appreciation of the importance to be accorded to the customs and particular laws of peoples in relation to common law, affirming that the authority of civil laws arises from the consent and usage of the peoples. He also criticizes the bad habit of giving authority to juridical doctrines on the basis of the arithmetical number of adherents, maintaining instead that what should be considered is not the number but the quality of the doctors and the quality of their foundations and reasoning.
To him are also attributed the *Instituta civilia*, an institutional work in imitation of Justinian’s, published posthumously under the care of Crescimbeni and, like the *Dottor volgare*, containing references to the larger work of the *Theatrum*.
D. L. reveals an open mind and a brilliant spirit not devoid of caustic irony, with a broad and modern outlook on juridical problems. His works are distinguished by their great canonical innovation, and on the other hand the very application of civil law is treated with that spirit of canonical equity which had its particular efficacy and natural seat in the tribunals of the State of the Church, above all in that of the Roman Rota.