Doctrine on the nature of language and dumbness in Bachelor Lasso's Legal Treatise on the dumb This article studies in its context, the Tratado Legal sobre los mudos [Legal Treatise on the dumb], which was written by Licenciado Lasso in the Oña Monastery (Burgos, Spain) in 1550. Lasso had moved there to observe the Benedictine monk, Pedro Ponce de León's methods for teaching the dumb children of the nobility. With these data as a reference, Lasso develops a theory of language and dumbness, which he applies as a jurist to the ability to inherit of those born dumb that learn how to speak. That theory is the central objective of the present study. Lasso did not edit his work, but it did not go unnoticed. The manuscript was published in the early twentieth century, in 1916, by Faustino Barberá and by Álvaro López Núñez in 1919, at a time when the social and health status of children, and in particular that of the deaf and dumb, was subject of renewed concern on behalf of the public administration in Spain.